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Waste Tyres can Improve the Seismic Performance of Integral Abutment Bridges

By
Ubani Obinna
-

Reuse of about 1.5 billion waste tyres that are produced annually worldwide inspired this research on the behaviour of rubberised backfills for integral abutment of bridges under seismic action. The joint research was carried out by authors from the School of Engineering, Aristotle University, Thessaloniki Greece; Energy Management Division, Siemens A.G., Erlangen, Germany; and Department of Civil and Environmental Engineering, University of Surrey, Guildford, UK, and was published by the Bulletin of Earthquake Engineering (Springer).

The research was conducted on the basis of parametric analysis, which aimed to evaluate the influence of different rubber-soil mixtures on the dynamic response of the abutment backfill system under various seismic excitations, accounting for dynamic soil-abutment interaction. Previous research has shown that the use of rubber-soil mixtures is a beneficial solution for foundations, embankments, backfilling in retaining walls, and other geotechnical works.

In the research, three different backfill materials were examined; the conventional, as per the representative backfilling material, which is common in European bridges, and two rubber-soil mixtures with varying percentage of rubber content. The conventional backfill is non-cohesive soil comprising of dry river sand.

The rubberised soil comprised of sand and recycled rubber in varying proportions per weight. The rubber content is in the form of granulated rubber produced by mechanically shredded waste tyres. Mixtures of composition 90% sand and 10% rubber (referred here as 90–10) or 70 % sand and 30 % rubber (referred here as 70–30) by weight were considered in the study.

A numerical integral abutment bridge model was modelled on Plaxis software and subjected to seismic action according to Eurocode 8.

Some of the improvements observed obtained are as follows;

(1) When compared with a conventional backfill, the settlements were reduced on average by 50% – 55%.

(2) The displacement of the abutment, and therefore the loading and stresses introduced to the prestressed deck was successfully reduced when rubberised backfills were used in comparison to the displacements of the conventional one. On average, it was reduced by about 8 % in the backfill 90–10 and by 18 % in the backfill 70–30.

(3) Similarly, the residual horizontal displacement of the top of the abutment was effectively reduced by 20 % in the backfill 90–10 and by 43 % in the backfill 70–30.

(4) The pressures acting on the abutment were dependent on the rubber content of the backfill, as an average reduction of 31 and 47 % was observed for the backfills 90–10 and 70–30, respectively, against the soil pressures calculated for the conventional scheme.

(5) The analyses showed that the internal forces of the abutment do not change significantly when the rubberized backfills were applied with respect to the conventional backfill.

However, the dynamic response of the abutment is a complicated mechanism that includes material and geometrical non-linearities, thus, analysis of the entire bridge system with the backfill soil should be conducted to better understand the behavior of integral abutment bridges.

For the full research paper;

Argyroudis S., Palaiochorinou A., Mitoulis S., Pitilakis D. (2016): Use of rubberised backfills for improving the seismic response of integral abutment bridges. Bulletin of Earthquake Engineering (2016) 14:3573–3590. DOI: https://doi.org/10.1007/s10518-016-0018-1

For more information on the work of the authors in providing innovative solutions for building resilience into critical infrastructure toward sustainable development. Visit their website INSFRASTRUCTURESILIENCE

Design for Fensheng 101 Skyscraper Unveiled

By
Ivy Ugorji
-

The design for the Fensheng 101 Skyscraper has been unveiled by GWP Architects. The project has a total construction area of approximately 81,000 square meters and a height of 200 meters. Located next to Lixin Avenue in Zengcheng, Guangzhou the building has been imagined to be a mixed development comprising of hotels, offices, apartments, and commercial stores. The north side overlooks Nanxiang Mountain and the south side overlooks Guangzhou Pearl River New City.

GWP5

The architectural concept of the building has been inspired by the image of sailing. The shape is generated with the core of the building as the axis, divided into two parts from north to south. Down the trend, it lightly fell on the podium to form a canopy space, cleverly integrated the podium and the tower of the building, and dotted the city’s skyline in a natural and organic form. With a shape demonstrating stability and wind resistance, the curved façade and roof also save the whole building a great deal of structural cost compared to the traditional tower structure.

GWP1

“The building introduces the concept of riding with the wind and sailing. Integrating form, space experience, ventilation, and lighting to create a unique architectural aesthetic. It aims to bring locals the joy of space perception and spiritual inspiration, as well as a sense of belonging to the place they live and work,” said Zhang Guowei, Chief Architect of FengSheng 101, GWP Partner.

GWP2

Structural Concept

The structural design of the building has been fully integrated with its elegant form, and was designed by RBS Architectural Engineering Design Associates. The building has two supporting blocks and a central core. With a precise control of the aspect ratio of the building and the core, the structural stability and wind resistance is enhanced. The curved facade and roof not only effectively reduces the wind load of the high-rise, but also saves the whole building a great deal of structure cost through improved aerodynamics.

GWP3

Building Facts

Official Name – Fengsheng 101
Name of Complex – Fengsheng 101
Structure Type – Building
Status – Under Construction
Country – China
City – Guangzhou
Street Address & Map – Lixin Highway, Zengcheng
Building Function – hotel / office
Construction – Start 2019
Completion – 2022

Architect Design – GWP Architects
Architect of Record – Mobozhi Architecture Design Inc.
Structural Engineer Design – RBS Architectural Engineering Design Associates
Project Manager – Guangzhou Wangtat Project Management & Consultant Co. Ltd.
Main Contractor – China Construction Second Engineering Bureau Ltd.


Other Consultants
• Civil AECOM
• Marketing InterContinental Hotels Group

Disclaimer: All images here are copyright properties of GWP Architects

Definition of a Tall Building | High-Rise Building

By
Ubani Obinna
-

The term ‘tall building’ is relative to the environment under consideration. A four-storey building located among bungalows in an area will easily be described as a tall building in the neighbourhood, and it will be an unarguable assertion. It is like the case of a one-eyed man being a king in the land of the blind.

According to Bungale (1988, 2010), tall buildings cannot be defined in terms of any specific number of floors or storey height, but the dividing line should be where the design of the structure moves from the field of statics to structural dynamics.

Council on Tall Buildings and Urban Habitat (2016) defined a building as being a high rise when it is considerably higher than the surrounding buildings or its proportion is slender enough to give the appearance of a tall building.

It is very typical for town planning agencies of municipals, regulatory bodies, standards organisations, and communities to come up with definitions and guidelines on what constitutes a high rise building in their jurisdictions.

For instance, the Tall Building Guidelines of the Town of Milton (2018), Canada, defined a tall building as a building whose height is greater than the adjacent street right of way or the wider of two streets if the building is located at an intersection. The right of way widths in Milton includes 35 m Arterials and 47 m Regional Roads, which means that tall buildings will start at about 11 storeys. But the guideline document acknowledges that a building of 9 storeys will be considered relatively tall, and hence the tall building guidelines should be applied wherever the building appears tall in relation to its context.

Old Oak and Park Royal Development Corporation (OPDC, 2018) in London defined a tall building as a building that is above 48 m (say 15 storeys) above the ground level.

The City of Burlington (2017) in Canada defined a tall building as building with over 11 storeys.

In Russia, tall buildings are those which are at least 75 m high (Generalov et al., 2018).

According to CTBUH, buildings of 300 to 600 meters are recognized as Supertall Skyscrapers, and those over 600 meters are recognized as Megatall Skyscrapers.

The National Building Code of India (2005) defined a high-rise building as a building having a height of more than 15 m (about 5 storey building).

There is no definition or guidance for high-rise or tall building in the National Building Code of Nigeria (2006). Lagos State Urban and Regional Planning Development Law (LSURPD, 2005) defined a high-rise building as a building with more than five floors (including the ground floor) and/or whose height exceeds 12 m from the ground level.

Summarily, according to Czyńska (2018);

“There is no unambiguous definition of the tall building (skyscraper) in the world. In the US, a skyscraper is considered to be a building exceeding the height of 150 m; in many European countries, this height is much smaller – 35 m. In Poland, technical regulations define two types of tall buildings: high ones (from 25 to 55 m), and high-rise buildings (55 m above the ground level). … a tall building is one that dominates in the landscape through its scale – so it does not have to be significantly high, but it is clearly above the surrounding buildings”.

Czyńska (2018)

From structural engineering perspective, a building can be described as a tall building as soon as the effects of lateral forces start getting significant on the behaviour and stability of the structure (Islam and Islam, 2014).

In a view shared by numerous authors (Bungale, 1988; Hoogendoorn, 2009; Bungale, 2010; Ali and Hamed, 2011; Carpinteri et al., 2012; Aly and Abburu, 2015; Longarini et al., 2017), as a building increases in its height, the forces of nature like wind and earthquake begin to dominate the structural systems, and impact on the structural behaviour of the building more than gravity forces.

Hence, engineers are concerned about choosing and designing structural systems that will be able to resist lateral and gravity loads, and at the same time meet other serviceability requirements of high rise buildings.

References

Ali B., and Hamed N. (2011): Loading pattern and spatial distribution of dynamic wind load and comparison of wind and earthquake effects along the heights of tall buildings. Proceedings to the 8th International Conference on Structural Dynamics, Leuven Belgium

Aly M.M., and Abburu S. (2015): On the design of high-rise buildings for multi-hazard: Fundamental differences between wind and earthquake demands. Hindawi – Shock and Vibrations (2015) Article ID 148681

Bungale S. T. (1988): Structural Analysis and Design of Tall Buildings. McGraw-Hill Book Company, New York

Bungale S. T. (2010): Reinforced Concrete Design of Tall Buildings. CRC Press, Taylor and Francis Group

Carpinteri A., Corrado M. , Laadogna G., and Cammarano S. (2012): Lateral load effects of tall shear wall structures of different heights. Structural Engineering and Mechanics 41(3):313-321

CTBUH – Council of Tall Buildings and Urban Habitat

Czynska K. (2018): A brief history of tall buildings in the context of cityscape transformation in Europe. Space and Form (36):281-296

Generalov V.P., Kalinkina N.A., and Zhadanova I.V. (2018): Typological diversity of tall buildings and complexes in relation to their functional structure. E35 Web of Conferences (33):1-8

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

Islam S., Islam M.M. (2014): Analysis on the structural systems for dripft control of tall buildings due to wind load: Critical investigations on building heights. The AUST Journal of Science and Technology 5(2):84-89

Lagos State Physical Planning and Development Regulations (2005): Lagos State Urban and Regional Planning Law. L.S.L.N. No 7

Longarini N., Cabras L., Zucca N., Chapain S., Aly A. M. (2017): Structural improvements for tall buildings under wind loads: Comparative study. Hindawi – Shock and Vibrations (2017) Article ID 2031248

National Building Code of India (2005) – Bureau of Indian Standards

National Building Code (2006): Federal Republic of Nigeria

ICE Announces Free Online Lecture Series for Members and Public

By
Ubani Obinna
-

The Institution of Civil Engineers (ICE), UK, has announced plans to commence free online lectures for members and general public. According to the information released on their website, the online lecture series is being launched to promote discussion of important challenges and issues facing civil engineers and the infrastructure sector.

It will be part of the ICE Strategy Sessions, a programme of free online lectures and events which bring together experts and industry leaders to discuss those thought leadership challenges.

The ICE Strategy Sessions will kick off on 21 April, with a lecture that considers whether civil engineers are doing enough to assure the public that the infrastructure they use is safe. Future events of the programme will explore how infrastructure can help achieve the UN Sustainable Development Goals (SDGs), and the role of the future engineer.

ICE will team up with global infrastructure software and solutions provider Bentley Systems to deliver the series, which is free to both the public and members. Using Bentley’s digital platform, the events will allow audiences to interact and ask questions in real-time. Audiences will also have access to a range of additional resources via ICE’s website.

First Event: Reassuring the public that infrastructure is safe
Date: 21 April, 2020
Time: 09:00 – 10:30 (UK time)

Key Speakers:
Dame Judith Hackitt
Government’s Independent Advisor on Tall Building Safety

Hazel McDonald
Chief Bridge Engineer at Transport Scotland

Julie Bregulla
Director of Fire & Building Technology at BRE

Speakers will present live and be followed by a live Q&A discussion.

To book your place at the event, click HERE

Reputable Journals in Geotechnical Engineering

By
Ubani Obinna
-

Geotechnical engineering is the application of engineering principles to the acquisition, interpretation, and use of knowledge of materials of the Earth’s crust and earth materials for the solution of engineering problems and the design of engineering works. It is concerned with the analysis, design and construction of foundations, slopes, retaining structures, embankments, tunnels, levees, wharves, landfills and other systems that are made of or are supported by soil or rock.

Knowledge in the field of geotechnical engineering is advanced through research publications in academic journals. Find below the list of reputable peer reviewed journals where you can publish your findings in the field of geotechnical engineering. This list is in no specified ranking order and will be updated/improved from time to time.

(A) CANADA
(1) Canadian Geotechnical Journal – (Canadian Publishing Science) – (Q1, Impact factor = 2.437, H Index = 100) https://www.nrcresearchpress.com/journal/cgj

(2) Canadian Journal of Civil Engineering – (Canadian Publishing Science) – (Q2, Impact factor = 0.742, H Index = 53)
https://www.nrcresearchpress.com/journal/cjce

(B) JAPAN
(3) Journal of JSCE – (Japan Society of Civil Engineers)
https://www.jstage.jst.go.jp/browse/journalofjsce/-char/en

(C) SPRINGER
(4) International Journal of Civil Engineering (Iranian Society of Civil Engineering) – (Q2, Impact factor = 0.624, H Index = 17)
https://link.springer.com/journal/40999

(5) Geotechnical and Geological Engineering Journal (Q1, H Index = 45)
https://link.springer.com/journal/10706

(6) International Journal of Geosynthetics and Ground Engineering
https://link.springer.com/journal/40891

(7) Asian Journal of Civil Engineering
https://link.springer.com/journal/42107

(8) Journal of the Institution of Engineers (India): Series A (Q2, H Index = 7)
https://link.springer.com/journal/40030

(9) Materials and Structures – Springer (Q1, Impact factor 2.458, H Index = 80)
https://link.springer.com/journal/11527

(10) KSCE Journal of Civil Engineering (Korean Society of Civil Engineers) – (Q2, H Index = 26)
https://link.springer.com/journal/12205

(11) Transportation in Developing Economies – Springer
https://link.springer.com/journal/40890

(12) Rock Mechanics and Rock Engineering – Springer (Impact factor = 4.100)
https://link.springer.com/journal/603

(13) Acta Geotechnica – Springer (Impact factor = 3.247)
https://link.springer.com/journal/11440

(14) Granular Matter – Springer
https://link.springer.com/journal/10035

(15) Bulletin of the Engineering Geology and the Environment (International Association of Engineering Geology and the Environment) – (formerly published as Bulletin of the International Association of Engineering Geology) Impact factor = 2.138
https://link.springer.com/journal/10064

(16) Transport in Porous Media – Springer (Impact factor = 1.997)
https://link.springer.com/journal/11242

(17) Transportation Infrastructure Geotechnology – Springer
https://link.springer.com/journal/40515

(18) International Journal of Pavement Research and Technology – Springer
https://www.springer.com/engineering/civil+engineering/journal/42947

(19) Innovative Infrastructure Solutions – Springer
https://link.springer.com/journal/41062

(20) Journal of Infrastructure Preservation and Resilience – Springer
https://jipr.springeropen.com/

(21) International Journal of Geo-engineering – Springer
https://link.springer.com/journal/40703

(22) Indian Geotechnical Journal – Springer
https://link.springer.com/journal/40098

(23) Frontiers of Structural and Civil Engineering – Springer (Impact factor = 1.272)
https://link.springer.com/journal/11709

(24) Earthquake Engineering and Engineering Vibration – Springer (Impacct factor = 1.050)
https://link.springer.com/journal/11803

(25) Soil Mechanics and Foundation Engineering – Springer (Impact factor = 0.376)
https://link.springer.com/journal/11204

(D) ASCE – American Society of Civil Engineers

(26) Journal of Construction Engineering and Management – ASCE
https://ascelibrary.org/journal/jcemd4

(27) Journal of Materials in Civil Engineering – ASCE
https://ascelibrary.org/journal/jmcee7

(28) Journal of Composites for Construction – ASCE
https://ascelibrary.org/journal/jccof2

(29) Journal of Highway and Transportation Research and Development – ASCE
https://ascelibrary.org/journal/jhtrcq

(30) Journal of Environmental Engineering – ASCE
https://ascelibrary.org/journal/joeedu

(31) Journal of Geotechnical and Geoenvironmental Engineering – ASCE
https://ascelibrary.org/journal/jggefk

(32) Journal of Transportation Engineering – ASCE
https://ascelibrary.org/journal/jtepbs

(33) International Journal of Geomechanics – ASCE
https://ascelibrary.org/journal/ijgnai

(34) Journal of Engineering Mechanics – ASCE
https://ascelibrary.org/journal/jenmdt

(E) TAYLOR AND FRANCIS ONLINE

(35) Soil and Sediment Contamination: An International Journal – T&Fonline (Impact factor = 0.992)
https://www.tandfonline.com/toc/bssc20/current

(36) Civil Engineering and Environmental Systems – T&Fonline (Impact factor =1.394)
https://www.tandfonline.com/toc/gcee20/current

(37) International Journal of Pavement Engineering – T&Fonline (Impact factor = 2.298)
https://www.tandfonline.com/toc/gpav20/current

(38) Structure and Infrastructure Engineering – T&Fonline (Impact factor = 2.430)
https://www.tandfonline.com/toc/nsie20/current

(39) Journal of Civil Engineering and Management – T&Fonline
https://www.tandfonline.com/toc/tcem20/current

(40) European Journal of Environmental and Civil Engineering – T&Fonline (Impact factor = 1.873)
https://www.tandfonline.com/toc/tece20/current

(41) Geomechanics and Geoengineering – T&Fonline
https://www.tandfonline.com/toc/tgeo20/current

(42) Road, Materials, and Pavement Design – T&Fonline (Impact factor = 1.980)
https://www.tandfonline.com/toc/trmp20/current

(43) Journal of Sustainable Cement Based Materials – T&Fonline
https://www.tandfonline.com/toc/tscm20/current

(45) International Journal of Sustainable Engineering – T&Fonline
https://www.tandfonline.com/toc/tsue20/current

(46) International Journal of Sustainable Transportation – T&Fonline (Impact factor = 2.586)
https://www.tandfonline.com/toc/ujst20/current

(47) International Journal of Geotechnical Engineering – T&Fonline
https://www.tandfonline.com/toc/yjge20/current

(48) Australian Journal of Civil Engineering – T&Fonline
https://www.tandfonline.com/loi/tcen20

(F) ELSEVIER
(49) International Journal of Pavement Research and Technology – (Has been transferred to Springer Nature)
https://www.journals.elsevier.com/international-journal-of-pavement-research-and-technology

(50) Case Studies in Construction Materials – Elsevier
https://www.journals.elsevier.com/case-studies-in-construction-materials

(51) Sustainable Cities and Society – Elsevier
https://www.journals.elsevier.com/sustainable-cities-and-society

(52) International Journal of Rock Mechanics and Mining Sciences – Elsevier
https://www.journals.elsevier.com/international-journal-of-rock-mechanics-and-mining-sciences

(53) Cement and Concrete Composites – Elsevier
https://www.journals.elsevier.com/cement-and-concrete-composites

(54) Construction and Building Materials – Elsevier
https://www.journals.elsevier.com/construction-and-building-materials

(55) Journal of Terramechanics – Elsevier
https://www.journals.elsevier.com/journal-of-terramechanics

(56) Transportation Geotechnics – Elsevier
https://www.journals.elsevier.com/transportation-geotechnics

(57) Geotextiles and Geomembranes – Elsevier
https://www.journals.elsevier.com/geotextiles-and-geomembranes

(58) Computers and Geotechnics – Elsevier
https://www.journals.elsevier.com/computers-and-geotechnics

(59) Soils and Foundations (Japanese Geotechnical Society) – Elsevier
https://www.journals.elsevier.com/soils-and-foundations

(60) Engineering Geology – Elsevier
https://www.journals.elsevier.com/engineering-geology

(61) Journal of Rock Mechanics and Geotechnical Engineering – Elsevier
https://www.journals.elsevier.com/journal-of-rock-mechanics-and-geotechnical-engineering/

(62) Soil Dynamics and Earthquake Engineering – Elsevier
https://www.journals.elsevier.com/soil-dynamics-and-earthquake-engineering

(G) INSTITUTE OF CIVIL ENGINEERS (ICE, UK)

(63) Environmental Geotechnics – ICE, UK
https://www.icevirtuallibrary.com/toc/jenge/current

(64) Geosynthetics International – ICE, UK
https://www.icevirtuallibrary.com/toc/jgein/current

(65) Geotechnical Research – ICE, UK
https://www.icevirtuallibrary.com/toc/jgere/current

(66) Géotechnique – ICE, UK
https://www.icevirtuallibrary.com/toc/jgeot/current

(67) Géotechnique Letters – ICE, UK
https://www.icevirtuallibrary.com/toc/jgele/current

(68) International Journal of Physical Modelling in Geotechnics – ICE, UK
https://www.icevirtuallibrary.com/toc/jphmg/current

(69) Journal of Environmental Engineering and Science – ICE, UK
https://www.icevirtuallibrary.com/toc/jenes/current

(70) Proceedings of the ICE – Geotechnical Engineering
https://www.icevirtuallibrary.com/toc/jgeen/current

(71) Proceedings of the ICE – Ground Improvement
https://www.icevirtuallibrary.com/toc/jgrim/current

(72) Proceedings of the ICE – Municipal Engineer
https://www.icevirtuallibrary.com/toc/jmuen/current

(73) Proceedings of the ICE – Municipal Engineer
https://www.icevirtuallibrary.com/toc/jmuen/current

(74) Proceedings of the ICE – Engineering and Computational Mechanics
https://www.icevirtuallibrary.com/toc/jencm/current

(75) Proceedings of the ICE – Engineering Sustainability
https://www.icevirtuallibrary.com/toc/jensu/current

(76) Proceedings of the ICE – Waste and Resource Management
https://www.icevirtuallibrary.com/toc/jwarm/current

(H) ASTM INTERNATIONAL JOURNALS
(77) Advances in Civil Engineering Materials (ACEM) – ASTM International
https://www.astm.org/DIGITAL_LIBRARY/JOURNALS/ACEM/index.html

(78) Geotechnical Testing Journal – ASTM International
https://www.astm.org/DIGITAL_LIBRARY/JOURNALS/GEOTECH/index.html

(79) Journal of Testing and Evaluation – ASTM International
https://www.astm.org/DIGITAL_LIBRARY/JOURNALS/TESTEVAL/index.html

(80) Materials Performance and Characterization – ASTM International
https://www.astm.org/DIGITAL_LIBRARY/JOURNALS/MPC/index.html

(I) INDERSCIENCE PUBLISHERS

(81) International Journal of Sustainable Materials and Structural Systems – Inderscience Publishers
https://www.inderscience.com/jhome.php?jcode=ijsmss

(82) International Journal of Microstructures and Material Properties – Inderscience Publishers
https://www.inderscience.com/jhome.php?jcode=ijmmp

(83) International Journal of Materials and Structural Integrity – Inderscience Publishers
https://www.inderscience.com/jhome.php?jcode=ijmsi

(84) International Journal of Materials Engineering Innovation – Inderscience Publishers
https://www.inderscience.com/jhome.php?jcode=ijmatei

(85) International Journal of Waste Management and Environment – Inderscience Publishers
https://www.inderscience.com/jhome.php?jcode=ijewm

(J) HINDAWI

(86) Advances in Civil Engineering – Hindawi
https://www.hindawi.com/journals/ace/

(87) Advances in Materials Science and Engineering – Hindawi
https://www.hindawi.com/journals/amse/

(K) WILEY ONLINE LIBRARY

(88) International Journal for Numerical and Analytical Methods in Geomechanics – Wiley Online

(89) Geomechanics and Tunnelling – Wiley Online

(90) Geotechnik – Wiley Online

(91) Near Surface Geophysics – Wiley Online

(92) Civil Engineering Design – Wiley Online

Compaction Pressure of Machines on Retaining Walls

By
Ubani Obinna
-

During the construction of earth retaining structures, it is very common to excavate the area, construct the earth retaining structure, backfill with the recommended material, and compact.

Pressure is exerted on the walls of the retaining structure during compaction, and some pressure is locked back in the soil after the machine is removed (that is why compaction pressure is usually treated as a permanent action).

The pressure on a wall retaining a compacted backfill is usually in excess of the one predicted using classical theory. The typical pressure distribution due to compaction is shown in Figure 1 according to Ingold (1979). Compaction pressure will be maximum up to a depth hc, after which it is locked into the pressure from the retained material. Therefore, pressure distribution at the back of a compacted retaining wall is not essentially triangular (in the absence of ground water).

Compaction Pressure distribution at the back of a retaining wall
Fig 1: Compaction Pressure Distribution on Retaining Walls (Based on Ingold, 1979)

The simplified method for evaluating the compaction pressure at the back of a retaining wall is given by the equations below;

Maximum horizontal pressure induced by compaction = √(2Qdγk,f)/π)

Zc = k √(2Qd)/(πγk,f)

hc = 1/k √(2Qd)/(πγk,f)

ph = kγk,fz

Where;
k = pressure coefficient (For retaining walls which can move forward sufficiently to mobilise active condition in the fill, k = ka. For unyielding rigid structures, k = ko)
γk,f = characteristic value of the density of the fill material
ph = horizontal pressure from the overburden stress
Qd = γFQk

Where;
γF = partial factor and
Qk = characteristic design compaction force (see Table 1 below)

For dead weight roller compactors, the effective line load is the weight of the roller divided by its roll width, and for vibratory rollers it should be calculated using an equivalent weight equal to the dead weight of the roller plus the centrifugal force generated by the roller’s vibrating mechanism. The centrifugal force may be taken to be equal to the dead weight of the roller in the absence of trade data. Typical values for different compaction machines are given in Table 1.

Table 1: Design force of Different Compaction Machines (Nayaranan and Goodchild, 2012)

Design force of different compacting equipment

Using the values from Table 1, the compaction pressure expected from the compacting machine can be calculated and incorporated into the design calculation.

References
(1) Ingold, T S (1979): The effects of compaction on retaining walls. Geotechnique 29(3), pp 265-283

(2) Narayanan R. S. and Goodchild C. H. (2012): Concrete Basements: Guidance on the design and construction of in situ concrete basement structures, London, UK: MPA – The Concrete Centre

Detailing of Columns to Eurocode 2

By
Peace Ikpotokin
-

It is important to carry out proper detailing after design of reinforced concrete columns. The requirements for column detailing is outlined in clause 9.5 of EN 1992-1-1:2004 (Eurocode 2). The basic recommendations for detailing of reinforced concrete columns according to Eurocode 2 are outlined below;

Main bars

(1) The longest side of the column (h) should not be greater than 4 times the shortest side (b), otherwise it is a wall.
h ≤ 4

(2) The smallest size of main reinforcements should be 8 mm
But according to the UK national annex, the minimum size of reinforcement φmin should be 12 mm

(3) The minimum area of reinforcement should be Asmin = 0.1NEd/fyd but not less than 0.002Ac

Where;
NEd = Design compressive axial force
fyd = Design yield strength of reinforcement = 0.87fyk
Ac = Cross sectional area of column

(4) The maximum area of reinforcement should not exceed 0.04Ac outside the lap areas. This limit should be increased to 0.08Ac at laps.

detailing at laps
Lapped joint of a column

(5) The minimum number of bars in a circular column should be 4.

(6) For columns having a polygonal cross-section, at least one bar should be placed at each corner.

Links

column links
Link spacing requirements in columns

(1) The diameter of the transverse reinforcement (links, loops or helical spiral reinforcement) should not be less than 6 mm or one quarter of the maximum diameter of the longitudinal bars, whichever is the greater.
φlinks = max (6 mm, φmax/4)

(2) All links should be anchored adequately.

(3) The spacing of links Scl,tmax should not exceed;
(a) 20 times the smallest diameter of longitudinal bars
(b) the smallest side of the column
(c) 400 mm
Scl,tmax = min(20φmax; b; 400)

(4) The maximum spacing required in 3 should be reduced by 0.6;
(a) in sections within a distance equal to the larger dimension of the column cross-section above or below a beam or slab;
(b near lapped joints, if the maximum diameter of the longitudinal bars is greater than 14 mm. A minimum of 3 bars evenly placed in the lap length is required.

(5) Where the direction of the longitudinal bars changes, (e.g. at changes in column size), the spacing of links should be calculated, taking account of the lateral forces involved. These effects may be ignored if the change of direction is less than or equal to 1 in 12.

(6) Every longitudinal bar or bundle of bars placed in a corner should be held by transverse reinforcement (links).

(7) No bar within a compression zone should be further than 150 mm from a restrained bar.

spacing of column links
Main bars should not be more than 150 mm from restrained bars

Thank you for visiting Structville today, and God bless you.

Deep Learning can be used to Detect Cracks in Fire Damaged Structures

By
Ubani Obinna
-

Researchers from Ewha Womans University, Seoul, South Korea, have proposed a machine learning technique for detecting surface cracks on fire damaged concrete. Even though concrete is known to possess good fire resistance, concrete structures are damaged when exposed to fire. Some of the defects usually observed when concrete is exposed to fire are change in colour, deflection, and cracking/spalling. Therefore, if a structure must be reused or repaired after a fire event, it is important to assess or investigate the extent of damage that has been done.

On the rationale for the study, the authors said,

One of the common investigation methods (of fire damaged structures) is optical observation of crack and deformation from the fire damaged structures. It would be cost effective if such optical observation is done quantitatively without requiring expensive testing machines or man power. Moreover, it would be very powerful if the crack information can be used as a guide to evaluate the performance of fire damaged concrete structures.

The authors employed a deep learning technique called Convolutional Neural Network (CNN) to detect surface cracks in fire damaged reinforced concrete beams. The results and findings were published in International Journal of Concrete Structures and Materials (Springer) in the year 2020. CNN is a deep learning technique that is primarily used for analyzing intricate structures of high-dimensional data such as high defnition (HD) images and videos. This method has been applied by some other researchers on damage assessment of concrete structures.

To carry out the study, the authors modelled five reinforced concrete beams of dimensions 250mm x 450mm x 5000 mm, reinforced with 3D19 at the bottom and 2D19 at the top. Moreover, stirrups of D10@150 c/c spacing were used to prevent shear failure when subjected to loading. The beams were subjected to variable fire duration/exposure time under sustained load, and heated according to the time-temperature curve developed by the International Standard Organisation.

Details of the specimen
Details of the specimen used in the study [Source [1]]

After the fire test, digital cameras were used to capture the surface of the concrete beams, and the images subjected to CNN architecture developed by the authors for training and testing. Subsequently, the study investigated the ratio of the number of pixels obtained from the CNN model to the crack length obtained from the optical observation, in order to see if consistency of the ratios can be found. It was observed that the ratios are almost same among the specimens having different variables. This tells that the proposed CNN method recognizes cracks of the fire damaged concrete beams from the surface images and follows similar changing tendencies of total crack lengths obtained from the optical observations.

CNN CRACK DETECTION ALGORITHM 2
Convolutional Neural Network Algorithm for Crack Detection (Source [1])

From their results, they concluded that the temperatures obtained from the thermocouples inside the beams are significantly related to total crack lengths of fire damaged beams rather than crack lengths at each zone. Also, they observed that there are strong relationships between the temperature and the number of pixels obtained from the proposed CNN model.

The limitation of the study is that the proposed CNN model is not able to capture crack depth and width. Nonetheless the number of pixels was found to be related to thermal-structural behaviors to some degree.

The findings of this article has been published on www.structville.com because it is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/

Reference
[1] Ryu E., Kang J., Lee J., Shin Y., Kim H. (2020): Automated Detection of Surface Cracks and Numerical Correlation with Thermal-Structural Behaviors of Fire Damaged Concrete Beams. International Journal of Concrete Structures and Materials 14(12). https://doi.org/10.1186/s40069-019-0387-3

Design of Counterfort Retaining Walls | Staad Pro

By
Ubani Obinna
-

Retaining walls are structures used for supporting earth materials at different levels. There are different types of retaining walls such as cantilever retaining walls, gravity retaining walls, counterfort retaining walls, buttressed retaining walls, etc. Counterfort retaining walls have similarities with cantilever retaining walls, with the difference of having triangular or rectangular web panels spaced at regular intervals at the back of the retaining wall.

These web panels are called counterforts, and they serve the purpose of tying the base slab and the wall (stem) together. By so doing, they reduce the internal stresses induced in the structure and increase the weight of the structure for stability. The main characteristic of a counterfort retaining wall is the inclusion of the counterforts.

counterfort retaining wall

These counterforts are positioned at regular intervals along the length of the wall, extending from the base to the top. They act as braces or buttresses, helping to distribute the lateral forces exerted by the retained soil.

The counterforts are connected to the main wall, known as the stem, by horizontal slabs or beams called tie beams. These tie beams create a robust structure, distributing the forces evenly and increasing the overall stability of the wall. The toe of the wall is typically thicker and wider than the stem, providing additional resistance against overturning and sliding.

The design of a counterfort retaining wall takes into account factors such as soil properties, anticipated loads, and water pressure. It must be designed to withstand the lateral pressure exerted by the retained soil and any potential surcharges, such as additional loads from adjacent structures or traffic.

One advantage of counterfort retaining walls is their ability to span longer heights compared to other types of retaining walls. The presence of counterforts and tie beams enhances the structural integrity, allowing for the construction of taller walls. This makes them suitable for applications where a high retaining wall is required, such as highway embankments, bridge abutments, and building foundations.

Another advantage is the ease of construction. Counterfort retaining walls can be built using precast concrete elements or cast-in-place methods, depending on the project requirements. The use of precast elements can expedite the construction process and reduce costs.

Counterfort retaining wall
Counterfort retaining wall

Modelling and Design of Counterfort Retaining Walls

Counterfort retaining walls can be easily modelled on Staad Pro software, and loaded to obtain the internal forces and deformations due to the retained earth. We are going to demonstrate that using the video below.

The data on the retaining wall is shown below;

loads on counterfort walls
Loads on counterfort retaining wall

Design Data
Height of wall from base = 7 m c/c
Length of base = 4.5m
Projection of toe = 0.8 m c/c
Projection of heel = 3.7 m c/c
Thickness of stem wall = 0.3 m
Thickness of base = 0.5 m
Thickness of counterfort = 0.3 m
Spacing of counterfort = 2.5 m c/c
Unit weight of concrete = 25 kN/m3
Unit weight of retained earth = 19 kN/m3
Angle of internal friction φ = 30°
Surcharge pressure on retaining wall = 10 kN/m2
Modulus of subgrade reaction of supporting soil = 50000 kN/m2/m

We are going to neglect the effect of passive earth pressure on the retaining wall.

COUNTERFORT RETAINING WALL MODEL
Model of counterfort retaining wall on Staad Pro

Coefficient of active earth pressure Ka = (1 – sinφ)/(1 + sinφ) = 0.333
Earth pressure at the back of the wall (triangularly distributed) = 0.333 x 19 kN/m3 x 7m = 44.289 kN/m2
Surcharge pressure at the back of the retaining wall = 0.333 x 10 = 3.33 kN/m2

Earth pressure on the base (heel) = (7m x 19 kN/m3) = 133 kN/m2
Surcharge pressure on the base (heel) = 10 kN/m2

Watch the video for the analysis of counterfort retaining walls on Staad Pro below;

Analysis Results

MX
Transverse bending moment under ULS load
MY
Longitudinal bending moment under ULS load
SQX
The transverse shear stress under ULS load
SQY
The longitudinal shear stress under ULS load

Displacement time history of a vibrating damped SDOF system

By
Ubani Obinna
-

Many engineering vibration problems can be idealised as single degree of freedom systems using mass-spring-dashpot model. In civil engineering, some water tank models and structures can be idealised this way for dynamic analysis such as the water tank shown above.

The ‘dashpot’ is the simplest mathematical element to simulate a viscous damper. The force in the dashpot under dynamic loading is directly proportional to the velocity of the oscillating mass.

Damped mass spring dashpot model 2
Mathematical model for free vibrating system with damping

For such structures under free vibration, the equation of motion is;

M.(d2z/dt2) + c(dz/dt) + kz = 0 ——— (1)

Where
M is the mass of the vibrating system
c is the coefficient of viscous damping expressed in force per unit velocity
k is the stiffness of the system
z is the displacement

There are three different type of solutions that can be obtained from equation (1); roots are real and negative, roots are equal, and roots are complex. The solution obtained can be used to describe the nature of damping of the system such as overdamped, underdamped, critically damped etc. For more information consult standard dynamics of structures textbook.

Solved Example
For the SDOF system shown below, plot the displacement time history analysis of the system for the initial conditions;
z = 0.1m, dz/dt = 0, at t = 0

solved

The equation of motion of the system can therefore be given by;

d2z/dt2 + 40(dz/dt) + 10000z = 0

x2 + 40x + 10000 = 0

The solution to the above equation has complex roots given by;
x = -20 ± 97.979i

The general solution to the equation is;
z = e-20t(A cos97.979t + B sin97.979t) —– (2)

From the initial conditions;
z(0) = 0.1 m
0.1 = e-20(0)[A cos97.979(0) + B sin97.979(0)]
0.1 = 1(A + 0)
Therefore A = 0.1

Hence;
z = e-20t(0.1cos97.979t + B sin97.979t) —- (2a)

Differentiating the equation (2a) using product rule;

For the first term of equation (2a);
u = 0.1e-20t; du/dt = -2e-20t

v = cos(97.979t); dv/dt = -97.979 sin(97.979t)

For the second term of equation (2a);
u = Be-20t; du/dt = -20Be-20t

v = sin(97.979t); dv/dt = 97.979 cos(97.979t)

Hence;
dz/dt = -2e-20tcos(97.979t) – 97.979e-20t sin(97.979t) – 20Be-20tsin(97.979t) + 97.979Be-20t cos(97.979t) — (3)

Applying the initial condition dz/dt = 0;
(0) = -2 + 97.979B
Therefore B = 2/97.979 = 0.02041

The equation of motion for the vibrating system is therefore;
z = 0.1e-20t cos(97.979t) + 0.02041e-20t sin(97.979t)

We can verify the solution by using Laplace Transform Method;
d2z/dt2 + 40(dz/dt) + 10000z = 0
z(0) = 0.1; dz/dt(0) = 0

S2ȳ – SX0 – X1 = d2z/dt2
Sȳ – X0 = dz/dt
ȳ = z

(S2ȳ – SX0 – X1) + 40(Sȳ – X0) + 10000ȳ = 0
X0 = 0.1
X1 = 0

(S2ȳ – 0.1S) + 40Sȳ – 4 + 10000ȳ = 0
⇒ S2ȳ + 40Sȳ + 10000ȳ = 4 + 0.1S
⇒ ȳ(S2 + 40S+ 10000) = 4 + 0.1S

Therefore ȳ = (4 + 0.1S)/(S2 + 40S+ 10000)

If we work on the denominator;
S2 + 40S + 202 = -10000 + 202
(S + 20)2 = -9600

What this implies is that;

z = (4 + 0.1S)/[(S + 20)2 + 9600] = [(0.1(S + 20) + 2)]/[(S + 20)2 + 9600]

z = [0.1(S + 20)]/[(S + 20)2 + 9600] + 2/[(S + 20)2 + 9600]
z = 0.1e-20t cos(40√6t) +2/(40√6t)e-20t sin(40√6t)

z = 0.1e-20t cos(97.979t) + 0.02041e-20t sin(97.979t)

When plotted on MATLAB between 0 and 1 seconds;

t = (0:0.001:1);
k = exp(-20.*t); z = k.*0.1.*cos(97.979.*t) + k.*0.02041.*sin(97.979.*t);
plot(t,z)

Displacement time graph

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