The idea of tall buildings has always been an exciting one to mankind. Towards the end of the 19th Century, the construction of tall buildings started in Chicago, due to new inventions such as the elevator and the telephone (Ali and Moon, 2007; Hallebrand and Jakobsson, 2016). Prior to the development of buildings for occupancy purposes, tall structures have been built in ancient times to satisfy one desire or another.
“They said to each other, “Come let us make bricks and bake them thoroughly”. They used brick instead of stone, and bitumen for mortar. Then they said, “Come let us build ourselves a city, with a tower that reaches to the heavens, so that we may make a name for ourselves and not be scattered over the face of the earth” – (Genesis 11:3 – 4)
In the quote above from the Bible, the quest for the construction of the Tower of Babel was driven by pride to reach towards the sky, and the quest to live together in one place. Other structures built in ancient times such as the Colossus of Rhodes, the Pyramids of Egypt (see Figure below), the Mayan temples of Mexico, and the Kutub Minar of India seems to have been determined by pride, ego, and competition (Bungale, 2010).
The Pyramids of Egypt (Choi, 2009)
The Pyramids of Egypt were constructed around 2500 BC as tombs for Pharaohs and stood at about 140 m tall. These ancient tall structures were not used as human habitats but were monuments and places of worship (Khanna and Chand, 2019).
In the Middle Ages between 11th and 13th centuries, tall towers were used in the town of San Gimignano, Italy, for defence (see below), but were later used as residential buildings (Hoogendoorn, 2009; Czyńska, 2018). Even though most of the structures have collapsed, some of them have been preserved on the skylines of the city, with the tallest towers exceeding a height of about 50 m. For this reason, San Gimignano is called the medieval Manhattan (Czyńska, 2018).
San Gimignano, Italy
Until the mid 19th century, gothic cathedrals were some of the tallest facilities in the world (Czyńska, 2018). In Europe, the construction of cathedrals led to the establishment of a quasi-religious status for the masons who were designing these amazing structures. For instance, the Cologne Cathedral was begun in 1248, and the masons used their knowledge to build a structure that must have installed awe in all who looked upon her (Gustaffson and Hehir, 2005).
Due to the limitations associated with construction of tall buildings using materials such as timber and bricks, builders began to look for alternative materials. The industrial revolution provided the materials such as wrought iron and steel. This also provided the social impetus for building higher as more workers from the countryside were required to work in the factories, so houses had to be provided for them (Gustaffson and Hehir, 2005).
Increased use of cast iron and later steel allowed the development of new architectural forms, such as long span roofs and bridges (Czyńska 2018). The result was the iron/steel frame structure which minimized the depth and width of the structural members at building perimeters (Ali and Moon, 2007).
The term high-rise began to be used to describe tall buildings and with the development in steel production and elevator, ever higher, buildings were being built. The first steel frame structure, Rand-McNally Building in Chicago was built in 1889 and was 10 storeys high (Smith and Coull, 1991).
The symbolic power of skyscrapers being recognized, a notable phenomenon occurred from the turn of the century. A skyscraper height race began, starting from the Park Row Building in New York, which had already reached 30 stories in 1899. This height race culminated with the completion of the 102-storey tall Empire State Building in 1931.
The Empire State Building
In terms of structural systems, most tall buildings in the early twentieth century employed steel rigid frames with wind bracing. Among them are the renowned Woolworth Building of 1913, Chrysler Building of 1930 and Empire State Building of 1931 all in New York (Ali, 2005). Their enormous heights at that time were accomplished not through notable technological evolution, but through excessive use of structural materials. Due to the absence of advanced structural analysis techniques, they were quite over-designed (Ali and Moon, 2007).
The early stages of American architecture lacked truly monumental structures. The monumental idea was gradually added to American architectural forms, reaching its apex with the construction of the Rockefeller Center in New York City (see below). The center represented a new concept of building a city within a city, containing a towering 60-storey structure surrounded by a number of smaller high-rise office buildings and recreational facilities.
The Rockefeller Center, New York City
This complex of skyscrapers has exercised increased influence since 1931, the year work on the Center was started. The building represents a departure in architectural thinking from a single-use, single-building concept to multi-use, multi-complex structures on a community scale.
Because of that practical example, American architectures responded more and more creatively to such demands and integration of city and the surrounding region. Another example of multi-building planning is the now nonexistent World Trade Center in New York City that consisted of twin 110-story towers and four smaller buildings grouped around a plaza (Bungale, 2010).
From 1950 to the mid-1960s, the International Style of architecture was embraced by prominent American architects and resulted in sleek boxlike glass and concrete or steel high-rises which integrated the concept of purity of design into the architecture of the structure. Notable examples are the Seagram Building (1950) and the Whitney Museum (1966), both in New York City, and the John Hancock Center (1968) in Chicago.
During the mid-1960s a reaction developed to the International Style that emphasized greater freedom of design. Figuratively speaking, the concept of glass box was beginning to shatter. It was no longer wrong to hide a structure behind a more aesthetic exterior.
The building and construction industry saw the advent of new forms of structural and other materials which allowed greater scope for aesthetic expression and innovation. Within the last two decades many major cities have had imaginative new shapes thrusting above their skylines using plan shapes that are other than prismatic (Bungale, 2010).
During the nineties, Asia started to take over the historically leading roles of tall buildings from the United States. New tall buildings have been built in a short period of time in the Far East and the Middle East (Hoogendoorn, 2009). The bank of China with a height of 267 m was completed in the year 1989 in Hong Kong, while the Jin Mao Tower in Shanghai with a height of 421 m was completed in the year 1998.
The Malaysian Petronas Towers in Kuala Lumpur with a height of 452 m was completed in the year 1999. As at 2004, the tallest building in the world was the Taepei 101 in Taiwan with a height of 508 m. Currently, the tallest building in the world remains the Burj Khalifa in Dubai with a height of 829.8m.
Chart of the world’s tallest buildings (www.wikipedia.org)
According to www.skyscrapercentre.com, the year 2020 yielded 106 completions of buildings 200 meters and taller, a 20 percent decline from 133 in 2019, and nearing a level last seen in 2014, when 105 such buildings were constructed. This is the second year in a row in which the completion figure declined. The tallest building to complete in 2020 was Central Park Tower in New York City, at 472 meters. This is the first time in five years in which the tallest completed building was not in China, and the first time since 2014, when One World Trade Center completed, that the tallest building of the year was in the United States. This is also the first year since 2014 in which there has not been at least one building taller than 500 meters completed.
References Ali, M.M. (2005): The skyscraper: Epitome of human aspirations. In Proceedings of the 7th World Congress of the Council on Tall Buildings and Urban Habitat: Renewing the Urban Landscape [CD-ROM]. Chicago, IL: Council on Tall Buildings and Urban Habitat. Ali M.M., and Moon K.S. (2007): Structural developments in tall buildings: Current trends and future prospects. Architectural Science Review 50(3):205-223 Bungale S. T. (2010): Reinforced Concrete Design of Tall Buildings. CRC Press, Taylor and Francis Group Choi Hi Sun (2009): Super tall building design approach. Proceedings to the American Institute of Architects Continuing Education Program Czynska K. (2018): A brief history of tall buildings in the context of cityscape transformation in Europe. Space and Form (36):281-296 Gustaffson D., and Hehir J. (2005): Stability of tall buildings. M.Sc thesis submitted to the Department of Civil and Environmental Engineering, Chalmers University of Technology, Sweden Hallebrand E., and Jakobsson W. (2016): Structural design of high-rise buildings. M.Sc thesis presented to the Department of Construction Sciences (Division of structural mechanics), Lund University, Sweden Hoogendoorn P.P (2009): Lateral load design of tall buildings: Evaluation and comparison for tall buildings in Madrid, Spain. M.Sc thesis presented to the Department of Civil Engineering and Geosciences, Delft University of Technology Khanna N., and Chand J. (2019): Optimum structural design for high rise buildings. International Journal ofInnovative Technology and Exploring Engineering 8(8):1469 – 1473 Smith, B.S. and Coull, A. (1991): Tall Building Structures: Analysis and Design. John Wiley & Sons, Inc. Singapore
For the cantilever beam loaded as shown above, which of the following diagram combinations will likely give the vertical deflection at point B based on y = 1/EI∫Mṁ ds ?
For the frame loaded as shown above, which of the following is the likely bending moment due to the externally applied unit load at point G? You are expected to analyse the structure by glancing atit without carrying out any physical calculation using pen, paper, or calculator.
Elsevier is undoubtedly one of the most renowned publishers of scientific and educational materials in the world. By offering the publication of textbooks, journals, and other services, they help advance research, information, and knowledge across several disciplines. According to their official website, the goal of Elsevier is to expand the boundaries of knowledge for the benefit of humanity.
If you have come up with a quality research article in Civil Engineering, you may want to consider publishing it with Elsevier since most articles published by Elsevier are usually rated very high in the world. Furthermore, most of their journals support open access and closed access. For closed access (standard subscription journals), your research article will be published free of charge by the journal, but access will be restricted to those who subscribe to the journal or those who are willing to purchase it. If you choose to publish it as open access (freely accessible to anyone), then you may have to pay for the publication.
In the list below, we are going to show different journals published by Elsevier that covers civil engineering topics or other related disciplines;
(1) Journal of Ocean Engineering and Science Journal of Ocean Engineering and Science (JOES) provides a medium for the publication of original research and latest development work in the field of ocean science and technology.
(2) Structures Structures aims to publish internationally-leading research across the full breadth of structural engineering. Papers for Structures are particularly welcome in which high-quality research will benefit from wide readership of academics and practitioners such that not only high citation rates but also tangible industrial-related pathways to impact are achieved.
(3) Case Studies in Construction Materials Case Studies in Construction Materials provides a forum for the rapid publication of short, structured Case Studies on construction materials and related Short Communications, specialising in actual case studies involving real construction projects.
(4) Water Resources and Industry Water Resources and Industry is one of a series of specialist titles launched by the highly-regarded Water Research. This journal moves research to innovation by focusing on the role industry plays in the exploitation, management and treatment of water resources.
(5) Sustainable Cities and Societies Sustainable Cities and Society (SCS) is an international journal focusing on fundamental and applied research aimed at designing, understanding, and promoting environmentally sustainable and socially resilient cities.
(6) Water Science and Engineering Water Science and Engineering journal is an international, peer-reviewed research publication covering new concepts, theories, methods, and techniques related to water issues.
(7) International Journal of Rock Mechanics and Mining Sciences This journal is concerned with original research, new developments, site measurements and case studies in rock mechanics and rock engineering. It provides an international forum for the publication of high quality papers on the subject of rock mechanics and the application of rock mechanics principles and techniques to mining and civil engineering projects built on or in rock masses.
(8) Cement and Concrete Composites This journal is designed to reflect current developments and advances being made in the general field of cement-concrete composites technology and in the production, use, and performance of cement-basedconstruction materials.
(9) Engineering Analysis with Boundary Elements This journal is specifically dedicated to the dissemination of the latest developments of new engineering analysis techniques using boundary elements and other mesh reduction methods.
(10) Marine Structures This journal aims to provide a medium for presentation and discussion of the latest developments in research, design, fabrication and in-service experience relating to marine structures, i.e., all structures of steel, concrete, light alloy or composite construction having an interface with the sea, including ships, fixed and mobile offshore platforms, submarine and submersibles, pipelines, subsea systems for shallow and deep ocean operations and coastal structures such as piers.
(11) Construction and Building Materials Construction and Building Materials provides an international forum for the dissemination of innovative and original research and development in the field of construction and building materials and their application in new works and repair practice. The journal publishes a wide range of innovative research and application papers which describe laboratory and to a limited extent numerical investigations or report on full scale projects.
(12) Finite Elements in Analysis and Design The aim of this journal is to provide ideas and information involving the use of the finite element method and its variants, both in scientific inquiry and in professional practice. The scope is intentionally broad, encompassing use of the finite element method in engineering as well as the pure and applied sciences.
(13) Thin-walled Structures Thin-walled structures comprises an important and growing proportion of engineering construction with areas of application becoming increasingly diverse, ranging from aircraft, bridges, ships, and oil rigs to storage vessels, industrial buildings and warehouses. The primary criterion for consideration of papers in Thin–Walled Structures is that they must be concerned with thin–walled structures or the basic problems inherent in thin-walled structures. Provided this criterion is satisfied no restriction is placed on the type of construction, material or field of application.
(14) Journal of Constructional Steel Research The Journal of Constructional Steel Research provides an international forum for the presentation and discussion of the latest developments in structural steel research and their applications. It is aimed not only at researchers but also at those likely to be most affected by research results, i.e. designers and fabricators.
(15) Engineering Structures Engineering Structures provides a forum for a broad blend of scientific and technical papers to reflect the evolving needs of the structural engineering and structural mechanics communities. Particularly welcome are contributions dealing with new developments or innovative applications of structural and mechanics principles and digital technologies for the analysis and design of engineering structures.
(16) Building and Environment Building and Environment is an international journal that publishes original research papers and review articles related to building science, urban physics, and human interaction with the indoor and outdoor built environment.
(17) Journal of Wind Engineering and Industrial Aerodynamics The objective of the journal is to provide a means for the publication and interchange of information, on an international basis, on all those aspects of wind engineering that are included in the activities of the International Association for Wind Engineering http://www.iawe.org/. These are; social and economic impact of wind effects; wind characteristics and structure, local wind environments, wind loads and structural response, diffusion, pollutant dispersion and matter transport, wind effects on building heat loss and ventilation, wind effects on transport systems, aerodynamic aspects of wind energy generation, and codification of wind effects.
(18) Computer Methods in Applied Mechanics and Engineering Computer Methods in Applied Mechanics and Engineering was founded over three decades ago, providing a platform for the publication of papers in advanced mathematical modeling and numerical solutions reflecting a combination of concepts, methods and principles that are often interdisciplinary in nature and span several areas of mechanics, mathematics, computer science and other scientific disciplines as well.
(19) Computers and Structures Computers & Structures publishes advances in the development and use of computational methods for the solution of problems in engineering and the sciences. The range of appropriate contributions is wide, and includes papers on establishing appropriate mathematical models and their numerical solution in all areas of mechanics.
(20) Cement and Concrete Research The aim of Cement and Concrete Research is to publish the best research on the materials science and engineering of cement, cement composites, mortars, concrete and other allied materials that incorporate cement or other mineral binders. In doing so, the journal will focus on reporting major results of research on the properties and performance of cementitious materials; novel experimental techniques; the latest analytical and modelling methods; the examination and the diagnosis of real cement and concrete structures; and the potential for improved materials.
(21) International Journal of Non-Linear Mechanics The International Journal of Non-Linear Mechanics provides a specific medium for dissemination of high-quality research results in the various areas of theoretical, applied, and experimental mechanics of solids, fluids, structures, and systems where the phenomena are inherently non-linear.
(22) Tunneling and Underground Space Technology Tunnelling and Underground Space Technology incorporating Trenchless Technology Research is an international journal which publishes authoritative articles encompassing original research and case studies on the development of tunnelling technology, the use of underground space and trenchless technology.
(23) Journal of Terramechanics The Journal of Terramechanics provides a forum for those involved in research, development, design, innovation, testing, application and utilization of off-road vehicles and soil working machinery, and their sub-systems and components. The Journal presents a cross-section of technical papers, reviews, comments and discussions, and serves as a medium for recording recent progress in the field.
(24) Transportation Geotechnics Transportation Geotechnics aims to publish high quality, theoretical and applied papers on all aspects of geotechnics for roads, highways, railways and underground railways, airfields and waterways.
(25) Automation in Construction Automation in Construction is an international journal for the publication of original research papers. The journal publishes refereed material on all aspects pertaining to the use of Information Technologies in Design, Engineering, Construction Technologies, and Maintenance and Management of Constructed Facilities.
(26) Geotextiles and geomembranes Geotextiles and Geomembranes fills this need and provides a forum for the dissemination of information amongst research workers, designers, users and manufacturers of geotextiles and geomembranes. By providing a growing fund of information the journal increases general awareness, prompts further research and assists in the establishment of international codes and regulations.
(27) Soils and Foundations Soils and Foundations is one of the leading journals in the field of soil mechanics and geotechnical engineering. It is the official journal of the Japanese Geotechnical Society (JGS)., The journal publishes a variety of original research paper, technical reports, technical notes, as well as the state-of-the-art reports upon invitation by the Editor, in the fields of soil and rock mechanics, geotechnical engineering, and environmental geotechnics.
(28) Soil Dynamics and Earthquake Engineering The journal aims to encourage and enhance the role of mechanics and other disciplines as they relate to earthquake engineering by providing opportunities for the publication of the work of applied mathematicians, engineers and other applied scientists involved in solving problems closely related to the field of earthquake engineering and geotechnical earthquake engineering.
(29) Advances in Water Resources Advances in Water Resources provides a forum for the presentation of fundamental scientific advances in the understanding of water resources systems. The scope of Advances in Water Resources includes any combination of theoretical, computational, and experimental approaches used to advance fundamental understanding of surface or subsurface water resources systems or the interaction of these systems with the atmosphere, geosphere, biosphere, and human societies.
(30) Journal of Building Engineering The Journal of Building Engineering (JOBE) is an interdisciplinary journal that covers all aspects of science and technology concerned with the whole life cycle of the built environment; from the design phase through to construction, operation, performance, maintenance and its deterioration. JOBE only publishes papers where significant scientific novelty is clearly demonstrated.
(31) Computers and Geotechnics Computers and Geotechnics provides an up-to-date reference for engineers and researchers engaged in computer-aided analysis and research in geotechnical engineering. The journal is intended for expeditious dissemination of advanced computer applications across a broad range of geotechnical topics. Contributions on advances in numerical algorithms, computer implementation of new constitutive models, and probabilistic methods are especially encouraged.
(32) Transportation Engineering Transportation Engineering will publish full research papers, review papers and short communications (new ideas, controversial opinions, proof of concept). The scope of Transportation engineering covers all as aspects of transport engineering, including both vehicle engineering (including automotive, aerospace, and naval) and civil engineering (planning, design, construction, maintenance, and operation for all type of systems infrastructures).
(33) Journal of Traffic and Transportation Engineering As an academic journal, the Journal of Traffic and Transportation Engineering (English Edition) provides a platform for the exchange and discussion of novel and creative ideas on theoretical and experimental research in the field of transportation. This journal publishes high-quality peer-reviewed papers on engineering, planning, management, and information technology for transportation.
(34) Composite Structures Composite Structures, an International Journal, disseminates knowledge between users, manufacturers, designers, and researchers involved in structures or structural components manufactured using composite materials.
(35) International Journal of Solids and Structures The International Journal of Solids and Structures has as its objective the publication and dissemination of original research in Mechanics of Solids and Structures as a field of Applied Science and Engineering. It fosters thus the exchange of ideas among workers in different parts of the world and also among workers who emphasize different aspects of the foundations and applications of the field.
(36) Journal of Fluids and Structures The Journal of Fluids and Structures serves as a focal point and a forum for the exchange of ideas, for the many kinds of specialists and practitioners concerned with fluid–structureinteractions and the dynamics of systems related thereto, in any field. One of its aims is to foster the cross-fertilization of ideas, methods and techniques in the various disciplines involved.
(37) Engineering Engineering is an international open-access journal that was launched by the Chinese Academy of Engineering (CAE) in 2015. Its aims are to provide a high-level platform where cutting-edge advancements in engineering R&D, current major research outputs, and key achievements can be disseminated and shared; to report progress in engineering science, discuss hot topics, areas of interest, challenges, and prospects in engineering development, and consider human and environmental well-being and ethics in engineering; to encourage engineering breakthroughs and innovations that are of profound economic and social importance, enabling them to reach advanced international standards and to become a new productive force, and thereby changing the world, benefiting humanity, and creating a new future.
(38) Development Engineering Development Engineering: The Journal of Engineering in Economic Development (Dev Eng) is an open access, interdisciplinary journal applying engineering and economic research to the problems of poverty. Published studies must present novel research motivated by a specific global development problem. The journal serves as a bridge between engineers, economists, and other scientists involved in research on human, social, and economic development.
(39) Alexandria Engineering Journal Alexandria Engineering Journal is an international journal devoted to publishing high-quality papers in the field of engineering and applied science. Alexandria Engineering Journal is cited in the Engineering Information Services (EIS) and the Chemical Abstracts (CA). The papers published in Alexandria Engineering Journal are grouped into five sections, according to the following classification:
• Mechanical, Production, Marine and Textile Engineering • Electrical Engineering, Computer Science and Nuclear Engineering • Civil and Architecture Engineering • Chemical Engineering and Applied Sciences • Environmental Engineering
(40) Engineering Failure Analysis Engineering Failure Analysis publishes research papers describing the analysis of engineering failures and related studies. Papers relating to the structure, properties and behaviour of engineering materials are encouraged, particularly those which also involve the detailed application of materials parameters to problems in engineering structures, components and design. In addition to the area of materials engineering, the interacting fields of mechanical, manufacturing, aeronautical, civil, chemical, corrosion and design engineering are considered relevant.
(41) Developments in the Built Environment Developments in the Built Environment (DIBE) is a new peer-reviewed gold open access (OA) journal whereby upon acceptance all articles are permanently and freely available. DIBE publishes original papers and short communications resulting from research in civil engineering and the built environment. This journal covers all topics related to construction materials and building sustainability, leading to a holistic approach that will benefit the community.
(42) Engineering Science and Technology, an International Journal Engineering Science and Technology, an International Journal (JESTECH) (formerly Technology), a peer-reviewed quarterly engineering journal, publishes both theoretical and experimental high quality papers of permanent interest, not previously published in journals, in the field of engineering and applied science which aims to promote the theory and practice of technology and engineering. In addition to peer-reviewed original research papers, the Editorial Board welcomes original research reports, state-of-the-art reviews and communications in the broadly defined field of engineering science and technology.
(43) International Journal of Engineering Science The International Journal of Engineering Science is not limited to a specific aspect of science and engineering but is instead devoted to a wide range of subfields in the engineering sciences. While it encourages a broad spectrum of contribution in the engineering sciences, its core interest lies in issues concerning material modeling and response. Articles of interdisciplinary nature are particularly welcome.
(44) Fire Safety Journal Fire Safety Journal is the leading publication dealing with all aspects of fire safety engineering. Its scope is purposefully wide, as it is deemed important to encourage papers from all sources within this multidisciplinary subject, thus providing a forum for its further development as a distinct engineering discipline. This is an essential step towards gaining a status equal to that enjoyed by the other engineering disciplines.
(45) Water Resources and Economics Water Resources and Economics is one of a series of specialist titles launched by the highly-regarded Water Research. For the purpose of sustainable water resources management, understanding the multiple connections and feedback mechanisms between water resources and the economy is crucial. Water Resources and Economics addresses the financial and economic dimensions associated with water resources use and governance, across different economic sectors like agriculture, energy, industry, shipping, recreation and urban and rural water supply, at local, regional and transboundary scale.
(46) Geomechanics for Energy and the Environment The aim of the Journal is to publish research results of the highest quality and of lasting importance on the subject of geomechanics, with the focus on applications to geological energy production and storage, and the interaction of soils and rocks with the natural and engineered environment. Special attention is given to concepts and developments of new energy geotechnologies that comprise intrinsic mechanisms protecting the environment against a potential engineering induced damage, hence warranting sustainable usage of energy resources.
Innovations, developments, and advancements in the civil engineering industry are primarily driven by research. Researches from scholars in different academic institutions, research institutes, and the industry are subjected to rigorous peer review before they are accepted and published in high ranking reputable journals. They are usually published as open access or closed access (standard subscription) journals.
Open access journals are journals that are publicly accessible to anyone. At Structville Integrated Services, we are interested in advancing civil engineering knowledge, and keeping civil engineers abreast of the latest industry standards, developments, and discoveries. Therefore, we have compiled a list of open access research articles by reputable journals for the month of January 2021. The list is not exhaustive and can never be. However, you can visit the website of the journals listed for more articles.
Any of the topics below that is of interest to you can be downloaded from the journal’s server by following the hyperlink provided on the title of the paper.
Self-compacting concrete (SCC) is a special type of concrete that has the ability to consolidate under gravity, fill up all required spaces, and produce dense and smoothly finished concrete when placed in formwork without the need for any external vibration. This special property of self-compacting concrete is due to the excellent workability it possesses in its fresh state, and the ability of the concrete to remain cohesive without segregation and bleeding when placed.
Self-compacting concrete was developed in Japan in the 1980s, and has found wide applications in the construction industry due to its numerous advantages. As a result of its highly flowable nature, SCC can settle into formworks and fill up heavily reinforced, congested, narrow, and deep sections by means of its own weight. Unlike conventional concrete, SCC does not require compaction using external force from mechanical equipment such as immersion vibrators.
Vibration is not required in self-compacting concrete
The common advantages of self-compacting concrete (SCC) are as follows;
Less labour is required for the vibration and compaction of concrete on site
Formwork congested with reinforcement can be cast with more ease
Narrow and/or deep forms can be cast without the formation of honeycombs
There is no risk of formwork damage due to vibration as commonly encountered in conventional concrete placement
There are reduced health and safety concerns on site
The working environment is improved due to little or no noise from concrete vibrating equipment
In many cases, self-compacting concrete is usually associated with high-strength concrete, hence the term ‘high-performance self-compacting concrete’ (HPSCC). High-performance self-compacting concrete can have compressive strength between 60 – 100 MPa. Ultra high-performance concrete can have compressive strength up to 150 MPa. High-performance concrete is expected to possess the following qualities;
High strength
High durability
Low shrinkage and creep
Easy to place and consolidate
Cost-effective
When compared with ordinary concrete, SCC is usually produced using a large amount of cement/fillers, superplasticizer, and/or other viscosity modifying admixtures. The supplemented binder content is associated with other cement replacement materials (CRMs) such as fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), rice husk ash (RHA), etc. The incorporation of CRMs is usually to improve the workability of the concrete, and the properties of the hardened concrete. There are limits to the size of aggregates also, with a recommended maximum aggregate size of 25 mm.
Therefore, for SCC, the following properties are required;
At the fresh state: Good workability without segregation
At the early state: No initial defects or honeycombs
At the hardened state: Good strength and resistance to external attacks
Tests for Self-Compacting Concrete
According to the European guidelines for self-compacting concrete, none of the test methods in the current EN 12350 series ‘Testing fresh concrete’ are suitable for the assessment of the key properties of fresh SCC. The filling ability and stability of self-compacting concrete in the fresh state can be defined by four key characteristics. Each characteristic can be addressed by one or more test methods as shown in the table below;
Characteristics
Preferred test
Flowability
Slump-flow test
Viscosity (assessed by rate of flow)
T500 Slump-flow test or V-funnel test
Passing ability
L-box test
Segregation
Segregation resistance (sieve) test
[Source: The European Guidelines for Self Compacting Concrete]
There are other appropriate tests that can be done on fresh SCC. Tests such as Orimet and O-funnel test can be used to assess the viscosity of SCC. U-box and J-ring tests can also be used to determine the passing ability of fresh SCC, while penetration and settlement column tests can also be used to determine the segregation resistance.
Slump-flow value describes the flowability of a fresh mix in unconfined conditions. It is a sensitive test that will normally be specified for all SCC, as the primary check that the consistence of the fresh concrete meets the specification. The slump flow value is usually obtained from the slup test.
Slump flow test
The viscosity of SCC can be assessed by the T500 time during the slump-flow test or assessed by the V-funnel flow time. The time value obtained does not measure the viscosity of SCC but is related to it by describing the rate of flow. Concrete with low viscosity will have a very quick initial flow and then stop. Concrete with high viscosity may continue to creep forward over an extended time.
V-funnel test
Passing ability describes the capacity of the fresh mix to flow through confined spaces and narrow openings such as areas of congested reinforcement without segregation, loss of uniformity, or causing blocking. In defining the passing ability, it is necessary to consider the geometry and density of the reinforcement, the flowability/filling ability, and the maximum aggregate size. This can be evaluated using the L-box test.
L-box test
Segregation resistance is fundamental for SCC in-situ homogeneity and quality. SCC can suffer from segregation during placing and also after placing but before stiffening. Segregation which occurs after placing will be most detrimental in tall elements but even in thin slabs, it can lead to surface defects such as cracking or a weak surface.
Segregation resistance becomes an important parameter with higher slump-flow classes and/or the lower viscosity class, or if placing conditions promote segregation. If none of these apply, it is usually not necessary to specify a segregation resistance class.
Consistency Requirements of Self-Compacting Concrete
Slump Flow
The European Guidelines for Self Compacting Concrete classifies the slump flow of SCC into;
SF1 (550 – 650 mm)
SF2 (660 – 750 mm), and
SF3 (760 – 850 mm).
SF1 (550 – 650 mm) is appropriate for unreinforced or slightly reinforced concrete structures that are cast from the top with free displacement from the delivery point (e.g. housing slabs), casting by a pump injection system (e.g. tunnel linings), and sections that are small enough to prevent long horizontal flow (e.g. piles and some deep foundations).
SF2 (660 – 750 mm) is suitable for many normal applications (e.g. walls, columns)
SF3 (760 – 850 mm) is typically produced with a small maximum size of aggregates (less than 16 mm) and is used for vertical applications in very congested structures, structures with complex shapes, or for filling under formwork. SF3 will often give a better surface finish than SF2 for normal vertical applications but segregation resistance is more difficult to control.
Viscosity
The viscosity of SCC is classified into:
VS1 (V-funnel time ≤ 8 seconds), and
VS2 (V-funnel time between 9 -25 seconds)
VS1/VF1 has good filling ability even with congested reinforcement. It is capable of self-levelling and generally has the best surface finish. However, it is more likely to suffer from bleeding and segregation.
VS2/VF2 has no upper class limit but with increasing flow time it is more likely to exhibit thixotropic effects, which may be helpful in limiting the formwork pressure or improving segregation resistance. Negative effects may be experienced regarding surface finish (blow holes) and sensitivity to stoppages or delays between successive lifts.
Passing Ability
It is important to define the confinement gap when specifying SCC. The defining dimension is the smallest gap (confinement gap) through which SCC has to continuously flow to fill the formwork. This gap is usually but not always related to the reinforcement spacing. Unless the reinforcement is very congested, the space between reinforcement and formwork cover is not normally taken into account as SCC can surround the bars and does not need to continuously flow through these spaces.
Examples of passing ability specifications are given below:
PA 1 structures with a gap of 80 mm to 100 mm, (e.g. housing, vertical structures)
PA 2 structures with a gap of 60 mm to 80 mm, (e.g. civil engineering structures)
With L-box test;
PA1 (≥ 0.80 with 2 rebars) PA2 (≥ 0.80 with 3 rebars)
For thin slabs where the gap is greater than 80 mm and other structures where the gap is greater than 100 mm no specified passing ability is required. For complex structures with a gap less than 60 mm, specific mock-up trials may be necessary.
Segregation Resistance
Segregation resistance of SCC is classified into;
SR1 (segregation resistance ≤ 20%), and
SR2 (segregation resistance ≤ 15%).
SR1 is generally applicable for thin slabs and for vertical applications with a flow distance of less than 5 metres and a confinement gap greater than 80 mm.
SR2 is preferred in vertical applications if the flow distance is more than 5 metres with a confinement gap greater than 80 mm in order to take care of segregation during flow. SR2 may also be used for tall vertical applications with a confinement gap of less than 80 mm if the flow distance is less than 5 metres but if the flow is more than 5 metres a target SR value of less than 10% is recommended.
Mix Design Approach for Self-Compacting Concrete
Laboratory trials should be used to verify the properties of the initial mix composition with respect to the specified characteristics and classes. If necessary, adjustments to the mix composition should then be made. Once all requirements are fulfilled, the mix should be tested at full scale in the concrete plant and if necessary at the site to verify both the fresh and hardened properties.
Mix design principles
To achieve the required combination of properties in fresh SCC mixes:
The fluidity and viscosity of the paste is adjusted and balanced by careful selection and proportioning of the cement and additions, by limiting the water/powder ratio and then by adding a superplasticiser and (optionally) a viscosity modifying admixture. Correctly controlling these components of SCC, their compatibility and interaction is the key to achieving good filling ability, passing ability and resistance to segregation.
In order to control temperature rise and thermal shrinkage cracking as well as strength, the fine powder content may contain a significant proportion of type l or ll additions to keep the cement content at an acceptable level.
The paste is the vehicle for the transport of the aggregate; therefore the volume of the paste must be greater than the void volume in the aggregate so that all individual aggregate particles are fully coated and lubricated by a layer of paste. This increases fluidity and reduces aggregate friction.
The coarse to fine aggregate ratio in the mix is reduced so that individual coarse aggregate particles are fully surrounded by a layer of mortar. This reduces aggregate interlock and bridging when the concrete passes through narrow openings or gaps between reinforcement and increases the passing ability of the SCC.
The mix design is generally based on the approach outlined below:
Evaluate the water demand and optimise the flow and stability of the paste
Determine the proportion of sand and the dose of admixture to give the required robustness
Test the sensitivity for small variations in quantities (the robustness)
Add an appropriate amount of coarse aggregate
Produce the fresh SCC in the laboratory mixer, perform the required tests
Test the properties of the SCC in the hardened state
Bridge pile caps are substructure elements that are used for transferring bridge superstructure load to the pile foundation. Pile caps for bridges are used for supporting the piers and/or the abutments of a bridge and are usually subjected to axial compression, shear (lateral force), and bending moment from the bridge pier or abutment.
These actions are usually resulting from the self-weight and superimposed dead loads on the bridge (permanent actions), vertical traffic live loads, horizontal actions due to wind, bridge deck contraction, impact/collision, braking, and skidding loads, etc.
Pile caps behave like thick plates and traditionally can be analysed using strut-and-tie or bending analogy method. Alternatively, finite element analysis can be used for the analysis of pile caps with or without the effects of soil-structure interaction.
It is possible to model pile caps using plates and beams on elements on Staad Pro software and obtain accurate results. Ubani has demonstrated the application of Staad Pro in the modelling of triangular pile caps (3 piles) and rectangular pile caps (2 piles) and compared the results with solutions from classical analysis methods. The results were found to be satisfactory for design purposes. The aim of this article is to extend the analysis of pile caps using Staad Pro to bridges and other complex structures (see the previous articles below).
In order to achieve this, the pile cap should be modelled using plate elements, while the piers (columns) and piles should be modelled using beam elements. In the case of pile caps supporting abutments, the abutment walls should be modelled using plate elements. It is very typical to model the piers/columns as stubs, and the actions applied to them as appropriate. The piles should be modelled as short columns that are supported with fixed supports. Furthermore, it is very important to ensure that all the nodes in the model are interconnected and rigid.
To demonstrate how this can be done, let us consider the pile cap of a bridge pier shown below. Note that the arrangement of the piles and pile caps should be consistent with the standard practice of ensuring that the maximum spacing of piles (for friction piles) should not less 3 times the diameter of the piles. The selection of the size and number of piles should be based on the geotechnical soil test report and the summation of the service loads from the superstructure.
For the bridge substructure shown above, the actions on each leg of the pier are as follows;
Horizontal Loads For road bridges, wind load need not be combined with braking/acceleration forces. Furthermore, accidental actions (collision) need not be considered with wind loads. (ULS) = 620 kN (SLS) = 496 kN
Bending moment; (ULS) = 2412 kNm (SLS) = 1647 kNm
The modelling of the pile cap on Staad Pro is shown below;
The reactions on the piles at SLS are shown below;
From the result above, the engineer should ensure that safe load bearing capacity of the each pile is not less than the maximum reaction on the pile (which is 1187.945 kN).
The bending moment on the pile cap at ultimate limit state is shown below;
The maximum reactions on the piles at ULS (for the sake of punching shear verification) is shown below;
The maximum reaction is 1624.341 kN and can be used for shear verification.
Timber joists are flexural horizontal timber members that are used for framing an open space in a building in order to support a floor or sheathing. They are usually closely spaced (usually between 400 – 800 mm) with the plane of maximum strength positioned vertically.
The spans of the joists are usually supported or intercepted by blockings which may be linear or skewed (staggered). Timber joists transfer the load of the floor to the vertical compression members (such as timber columns) and can be made of solid timber, glulam, or other engineered wood products.
As flexural structural members, the design of timber joists is expected to satisfy the following requirements;
Bending
Shear
Bearing
Lateral buckling
Deflection, and
Vibration
Design Example of Timber Joists
In this article, let us design the timber floor joists for a domestic dwelling using timber of strength class C24 to support a medium-term permanent action of 0.75 kN/m2 and a variable (live) load of 1.5 kN/m2 given that the:
a) floor width, b, is 3.6 m and floor span, l, is 3.0 m b) joists are spaced at 600 mm centres c) the bearing length is 100 mm
Self weight of timber = 3.4335 kN/m3 x 0.15m x 0.05m = 0.0257 kN/m Chaaracteristic permaent action on each joist = 0.75 kN/m2 x 0.6m = 0.45 kN/m Total characteristic permanent action gk = 0.476 kN/m
Total characteristic variable action qk = 1.5 kN/m2 x 0.6 m = 0.9 kN/m
At ultimate state; pEd = 1.35gk + 1.5qk = 1.9926 kN/m At serviceability limit state pEd = 1.0gk + 1.0qk = 1.376 kN/m
Structural Analysis
Structural Design Member – Span 1 The partial factor for material properties and resistances Partial factor for material properties (Table 2.3 of EN 1995-1-1:2004); γM = 1.300
Member details Load duration (cl.2.3.1.2 of EC5); Medium-term Service class – (cl.2.3.1.3 of EC5); 2
Timber section details Number of timber sections in member; N = 1 Breadth of sections; b = 50 mm Depth of sections; h = 150 mm Timber strength class – EN 338:2016 Table 1; C24
Properties of 50 x 150 mm timber section Cross-sectional area, A = 7500 mm2 Section modulus, Wy = 187500 mm3 Section modulus, Wz = 62500 mm3 Second moment of area, Iy = 14062500 mm4 Second moment of area, Iz = 1562500 mm4 Radius of gyration, iy = 43.3 mm Radius of gyration, iz = 14.4 mm
Timber strength class C24 Characteristic bending strength, fm.k = 24 N/mm2 Characteristic shear strength, fv.k = 4 N/mm2 Characteristic compression strength parallel to grain, fc.0.k = 21 N/mm2 Characteristic compression strength perpendicular to grain, fc.90.k = 2.5 N/mm2 Characteristic tension strength parallel to grain, ft.0.k = 14.5 N/mm2 Mean modulus of elasticity, E0.mean = 11000 N/mm2 Fifth percentile modulus of elasticity, E0.05 = 7400 N/mm2 Shear modulus of elasticity, Gmean = 690 N/mm2 Characteristic density, rk = 350 kg/m3 Mean density, rmean = 420 kg/m3
For the structure loaded as shown above, answer the following questions given below. Note that the use of calculators is discouraged. The aim of this question is to improve our ability to predict the expected behaviour of a structure by just glancing at them. Good luck to you.
[1] What is the maximum bending moment in member DE? (A) 0.5 kNm (B) 1.0 kNm (C) 2.0 kNm (D) 4.0 kNm
[2] What is the value of the shear force at point G, just to the right? (A) -1.5 kN (B) +3 kN (C) -3 kN (D) +1.5 kNm
[3] What is the value of the bending moment at point C, just to the right? (A) -3 kNm (B) 1.5 kNm (C) +3 kNm (D) -1 kNm
[4] What is the value of the bending moment, at point F? (A) -1 kNm (B) -2 kNm (c) -3 kNm (D) -4 kNm
A full torsional design covering the ultimate and serviceability limit states is required when the equilibrium of a structure is dependent on the torsional resistance of the member. Reinforced concrete (RC) beams are subjected to torsion when the point of application of loads does not coincide with the shear centre of the beams. This can be due to the arrangement of the beams or the loading pattern as can be found in circular or canopy beams.
Fig 1: Typical examples of beams subjected to torsion
According to clause 6.3.1(3) of EN 1992-1:2004, the torsional resistance of a section may be calculated on the basis of a thin-walled closed section, in which equilibrium is satisfied by a closed shear flow. Solid sections may be modelled by equivalent thin-walled sections. Complex shapes, such as T-sections, may be divided into a series of sub-sections, each of which is modelled as an equivalent thin-walled section, and the total torsional resistance taken as the sum of the capacities of the individual elements.
Fig 2: Notations and definitions for torsion in Eurocode 2 [Source: Figure 6.11, EN 1992-1-1:2004]
In Eurocode 2, the shear stress in a wall of a section subject to a pure torsional moment may be calculated from:
τt,itef,i = TEd/2Ak
The shear force VEd,i in a wall i due to torsion is given by:
VEd,i = τt,itef,izi
where; TEd is the applied design torsion Ak is the area enclosed by the centre-lines of the connecting walls, including inner hollow areas. τt,i is the torsional shear stress in wall i tef,i is the effective wall thickness. It may be taken as A/u, but should not be taken as less than twice the distance between edge and centre of the longitudinal reinforcement. For hollow sections the real thickness is an upper limit A is the total area of the cross-section within the outer circumference, including inner hollow areas u is the outer circumference of the cross-section zi is the side length of wall i defined by the distance between the intersection points with the adjacent walls
The required cross-sectional area of the longitudinal reinforcement for torsion ΣAsl may be calculated from Expression (6.28) of EC2:
ΣAsl/fyd = TEdcotθ/2Ak
where; uk is the perimeter of the area Ak fyd is the design yield stress of the longitudinal reinforcement Asl θ is the angle of compression struts
According to clause 6.3.2(4) of EC2, the maximum resistance of a member subjected to torsion and shear is limited by the capacity of the concrete struts. In order not to exceed this resistance the following condition should be satisfied:
where: TEd is the design torsional moment VEd is the design transverse force TRd,max is the design torsional resistance moment = TRd,max = 2ναcwfcdAktef,isinθcosθ VRd,max is the maximum design shear resistance according to Expressions (6.9) of EC2
Worked Example
Carry out a full torsional design of a rectangular reinforced concrete (RC) beam subjected to an ultimate torsional moment of 55 kNm, and shear force of 225 kN. The section is 600 x 400 mm, and reinforcement of 4H25 (As,prov = 1964 mm2) has been provided to resist the bending moment. (fck = 28 N/mm2; fyk = 500 N/mm2)
Beam dimensions Section width; b = 400 mm Section depth; h = 600 mm
Design forces Maximum design torsional moment; TEd,max = 55.0 kNm Maximum design shear force; VEd,max = 225.0 kN Area of design longitudinal reinforcement; Asl = 1964 mm2 Effective depth to outer layer; d = 450 mm
Fig 3: Equivalent thin-walled section
Torsional resistance (Section 6.3, EC2)
Effective thickness of walls – cl.6.3.2(1); tef,i = (b × h) / (2 × (b + h)) = 120 mm Area enclosed by centre lines of walls – cl.6.3.2(1); Ak = (b – tef,i) × (h – tef,i) = 134400 mm2 Perimeter – cl.6.3.2(3); Uk = 2 × ((b – tef,i) + (h – tef,i)) = 1520 mm
Required torsional reinforcement Required area of add. long. reinf. for torsion (6.28); Asl,req = TEd,max × Uk × cot(qt) / (2 × Ak × fyd) = 1788 mm2 Provide 10Y16 side bars (5 on each face) for torsion (Asprov = 2010 mm2)
The longitudinal bars should be arranged so there is at least one bar at each corner with the other spaced around the periphery of the links at a spacing of 350mm or less (cl.9.2.3(4))
Required shear reinforcement for torsion (one leg); Asw,req = TEd,max / (2 × Ak × fyd × cot(qt)) = 188 mm2/m Maximum spacing for torsion shear reinforcement; sw,max = min(Uk/8, b, h) = 190 mm
Provide 2 legs H10@175 c/c as torsion/shear reinforcement
[Featured Image Credit] Chai H.K., Majeed A.A., Allawi A.A (2015): Torsional Analysis of Multicell Concrete Box Girders Strengthened with CFRP Using a Modified Softened Truss Model. ASCE Journal of Bridge Engineering, 20(8) https://doi.org/10.1061/(ASCE)BE.1943-5592.0000621
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