Pub Date : 2022-09-14DOI: 10.17159/2309-8775/2022/v64n3a4
D. Willenberg, M. Zuidgeest, E. Beukes
Cape Town's Bus Rapid Transit (BRT) system, MyCiTi, uses an Automated Fare Collection (AFC) system that generates large volumes of transactional data on a daily basis. This data can be considered Big Data. The AFC data in its raw format, however, is incapable of supporting supply and demand analysis (e.g. studying bus occupancy rates). Agent-Based Modelling (ABM) can be used to analyse such data for that purpose. This paper discusses the development and calibration of a MATSim-based ABM to analyse AFC data for Cape Town's BRT system. It is shown that data-formatting algorithms are critical in the preparation of data for modelling activities. Furthermore, the development of appropriate ABM calibration parameters requires careful consideration in terms of appropriate data collection, simulation testing, and justification, which are discussed. The paper furthermore shows that the calibrated ABM can generate outputs such as bus on-board volumes, a system-demand overview, and even individual commuter path choice behaviour. Finally, a validation exercise shows that the model developed for this study is able to provide good estimates of on-board bus volumes (R2 = 0.85). It is, however, recommended that further research be conducted into studying agent path choices through simulation.
{"title":"Quantifying MyCiTi supply usage using Big Data and Agent-Based Modelling","authors":"D. Willenberg, M. Zuidgeest, E. Beukes","doi":"10.17159/2309-8775/2022/v64n3a4","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64n3a4","url":null,"abstract":"Cape Town's Bus Rapid Transit (BRT) system, MyCiTi, uses an Automated Fare Collection (AFC) system that generates large volumes of transactional data on a daily basis. This data can be considered Big Data. The AFC data in its raw format, however, is incapable of supporting supply and demand analysis (e.g. studying bus occupancy rates). Agent-Based Modelling (ABM) can be used to analyse such data for that purpose. This paper discusses the development and calibration of a MATSim-based ABM to analyse AFC data for Cape Town's BRT system. It is shown that data-formatting algorithms are critical in the preparation of data for modelling activities. Furthermore, the development of appropriate ABM calibration parameters requires careful consideration in terms of appropriate data collection, simulation testing, and justification, which are discussed. The paper furthermore shows that the calibrated ABM can generate outputs such as bus on-board volumes, a system-demand overview, and even individual commuter path choice behaviour. Finally, a validation exercise shows that the model developed for this study is able to provide good estimates of on-board bus volumes (R2 = 0.85). It is, however, recommended that further research be conducted into studying agent path choices through simulation.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49458883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-14DOI: 10.17159/2309-8775/2022/v64n3a1
G. Nganga, M. Alexander, Y. Ballim
Specifications for durability that are based on performance tests on concrete during the early stages of construction are finding acceptance throughout the world. In South Africa the durability index (DI) approach has been accepted into local specifications. This raises a challenge in the design of a concrete mixture for a construction project that takes account of the variability in materials and test conditions to ensure that the concrete will achieve the specification requirements when subjected to DI testing on in-situ samples. This paper proposes a statistical approach to accounting for this variability in concrete mixture design with oxygen permeability index (OPI) testing, in a manner that acknowledges the variability of both laboratory-based and in-situ sample testing for compliance. The OPI test results obtained on nominally similar concretes on actual construction projects undertaken by the South African National Roads Agency Limited (SANRAL), which included the DI-based specifications, were used to illustrate the operation of the proposed approach. The results show that the target value of OPI to be achieved in the design of concrete mixtures is influenced by the level of quality control on construction sites but that this can be managed through an appropriate statistical approach.
{"title":"Variability of oxygen permeability index values in concrete construction: A proposed approach for parameter margins to guide concrete mixture design","authors":"G. Nganga, M. Alexander, Y. Ballim","doi":"10.17159/2309-8775/2022/v64n3a1","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64n3a1","url":null,"abstract":"Specifications for durability that are based on performance tests on concrete during the early stages of construction are finding acceptance throughout the world. In South Africa the durability index (DI) approach has been accepted into local specifications. This raises a challenge in the design of a concrete mixture for a construction project that takes account of the variability in materials and test conditions to ensure that the concrete will achieve the specification requirements when subjected to DI testing on in-situ samples. This paper proposes a statistical approach to accounting for this variability in concrete mixture design with oxygen permeability index (OPI) testing, in a manner that acknowledges the variability of both laboratory-based and in-situ sample testing for compliance. The OPI test results obtained on nominally similar concretes on actual construction projects undertaken by the South African National Roads Agency Limited (SANRAL), which included the DI-based specifications, were used to illustrate the operation of the proposed approach. The results show that the target value of OPI to be achieved in the design of concrete mixtures is influenced by the level of quality control on construction sites but that this can be managed through an appropriate statistical approach.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47827531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-14DOI: 10.17159/2309-8775/2022/v64n3a6
L. Kemp, W. J. Steyn, M. P. Roux
This paper introduces the application of technology solutions into the realm of bridge inspection methodologies in South Africa, aiming to enhance the current visual bridge inspection methodology. Unmanned Aerial Vehicles (UAVs) can be used as an alternative to collect bridge image data, and point cloud models can be created from captured images by using photogrammetry software. For this study, accredited bridge inspectors were approached to complete TMH 19 inspection sheets of bridge structures using only the point cloud models and captured images, as a proposed new inspection methodology. This paper compares historic inspection ratings and the point cloud inspection ratings to investigate the effectiveness and practicality of the new proposed inspection methodology. The study concluded that bridge inspectors could identify and rate critical defects of bridge structures using the new inspection methodology, but there are limitations and specific use cases that need to be identified.
{"title":"Enhanced methodology for visual bridge inspections in South Africa","authors":"L. Kemp, W. J. Steyn, M. P. Roux","doi":"10.17159/2309-8775/2022/v64n3a6","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64n3a6","url":null,"abstract":"This paper introduces the application of technology solutions into the realm of bridge inspection methodologies in South Africa, aiming to enhance the current visual bridge inspection methodology. Unmanned Aerial Vehicles (UAVs) can be used as an alternative to collect bridge image data, and point cloud models can be created from captured images by using photogrammetry software. For this study, accredited bridge inspectors were approached to complete TMH 19 inspection sheets of bridge structures using only the point cloud models and captured images, as a proposed new inspection methodology. This paper compares historic inspection ratings and the point cloud inspection ratings to investigate the effectiveness and practicality of the new proposed inspection methodology. The study concluded that bridge inspectors could identify and rate critical defects of bridge structures using the new inspection methodology, but there are limitations and specific use cases that need to be identified.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48869681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-14DOI: 10.17159/2309-8775/2022/v64n3a3
J. A. Du Plessis, E. Braune
South Africa has a broadly developed water resource infrastructure, based mainly on surface water, localised groundwater, and limited desalination. The Department of Water and Sanitation projects that increasing requirements will exceed the capacity of the country's bulk water supply systems by 2025. To mitigate water scarcity at a local authority level, more conjunctive water use solutions need to be investigated. A Microsoft Excel 2016 model, estimating supply capacity on a daily basis, was developed for local authorities to better manage their water supply systems. The model utilises synthetically generated stochastic streamflow sequences, based on historical data. Monthly streamflow is disaggregated into daily streamflow and a rainfall-runoff relationship is established to produce synthetic rainfall sequences. Groundwater is modelled using an approach similar to the Aquifer Firm Yield Model. Recharge percentages (rainfall data) are obtained from the Groundwater Resource Assessment Phase 2 project. The Cooper-Jacob model evaluates borehole drawdowns and their effect on surrounding boreholes. Desalination and water reclamation are modelled as one source. The model evaluates and compares the historical, as well as stochastic available yield of a conjunctive use water supply system, for different operational scenarios. The water supply system of Stellenbosch was used as a case study to illustrate the model's functionality.
{"title":"A stochastic, daily time-step model for conjunctive water use at local authority level","authors":"J. A. Du Plessis, E. Braune","doi":"10.17159/2309-8775/2022/v64n3a3","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64n3a3","url":null,"abstract":"South Africa has a broadly developed water resource infrastructure, based mainly on surface water, localised groundwater, and limited desalination. The Department of Water and Sanitation projects that increasing requirements will exceed the capacity of the country's bulk water supply systems by 2025. To mitigate water scarcity at a local authority level, more conjunctive water use solutions need to be investigated. A Microsoft Excel 2016 model, estimating supply capacity on a daily basis, was developed for local authorities to better manage their water supply systems. The model utilises synthetically generated stochastic streamflow sequences, based on historical data. Monthly streamflow is disaggregated into daily streamflow and a rainfall-runoff relationship is established to produce synthetic rainfall sequences. Groundwater is modelled using an approach similar to the Aquifer Firm Yield Model. Recharge percentages (rainfall data) are obtained from the Groundwater Resource Assessment Phase 2 project. The Cooper-Jacob model evaluates borehole drawdowns and their effect on surrounding boreholes. Desalination and water reclamation are modelled as one source. The model evaluates and compares the historical, as well as stochastic available yield of a conjunctive use water supply system, for different operational scenarios. The water supply system of Stellenbosch was used as a case study to illustrate the model's functionality.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48641545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a6
C. Okoro, K. Lawani
Transportation systems are somewhat incomplete without integrating non-motorised transport (NMT) facilities to ensure safety, security, convenience, productivity and reduced environmental impact from such projects. This study examined the performance of NMT infrastructure and services provided to ensure smart transport and mobility in Johannesburg, South Africa. Two projects were identified as case studies, and a total of 21 semi-structured, open-ended interviews were conducted with residents and other road users in the vicinity of the projects to enable the acquisition of relevant information. Data was analysed using thematic content analysis supported with Atlas-ti software. Findings revealed that, although the facilities are in good condition and adequately maintained, the usage level is low. Incidents of poor safety and security were reported. Nevertheless, new value-added businesses operate along the routes and users indicated some satisfaction with their travel experience. To achieve value creation where NMTs are provided, it is crucial to ensure that the "smartness" of the cities is achieved and sustained. The practical implication of this study is the provision of invaluable information towards assisting road and NMT infrastructure stakeholders in improving the planning and delivery of sustainable transport infrastructure. Future studies will benefit from using more case study projects to strengthen these findings further and improve the generalisability.
{"title":"Optimising sustainable mobility: A performance assessment of non-motorised transport infrastructure in Johannesburg, South Africa","authors":"C. Okoro, K. Lawani","doi":"10.17159/2309-8775/2022/v64no2a6","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64no2a6","url":null,"abstract":"Transportation systems are somewhat incomplete without integrating non-motorised transport (NMT) facilities to ensure safety, security, convenience, productivity and reduced environmental impact from such projects. This study examined the performance of NMT infrastructure and services provided to ensure smart transport and mobility in Johannesburg, South Africa. Two projects were identified as case studies, and a total of 21 semi-structured, open-ended interviews were conducted with residents and other road users in the vicinity of the projects to enable the acquisition of relevant information. Data was analysed using thematic content analysis supported with Atlas-ti software. Findings revealed that, although the facilities are in good condition and adequately maintained, the usage level is low. Incidents of poor safety and security were reported. Nevertheless, new value-added businesses operate along the routes and users indicated some satisfaction with their travel experience. To achieve value creation where NMTs are provided, it is crucial to ensure that the \"smartness\" of the cities is achieved and sustained. The practical implication of this study is the provision of invaluable information towards assisting road and NMT infrastructure stakeholders in improving the planning and delivery of sustainable transport infrastructure. Future studies will benefit from using more case study projects to strengthen these findings further and improve the generalisability.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49624323","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a2
N. Fouché, P. Day
The sand-covered coastal plain connecting the Cape Peninsula mountain chain to the southwestern Cape mainland is known as the Cape Flats. The whitish windblown sands covering this area of approximately 460 km2, referred to as the Quaternary sands of the Cape Flats, provide founding for the rapid and ongoing development in the area. A knowledge of the geotechnical properties and engineering behaviour of these sands is essential for design of suitable foundations for proposed structures and earthworks associated with such developments. By combining, analysing and interpreting the wealth of existing and available geotechnical information from previous and new soil investigations undertaken in the area, the Quaternary-aged sands of the Witzand, Springfontyn and Langebaan Formations from the Cape Flats were characterised in terms of their physical properties and engineering behaviour. The sands from the study area were classified based on their grading, Atterberg limits, maximum dry density and optimum moisture content, minimum dry density, California Bearing Ratio (CBR), erodibility and corrosivity, and characterised in terms of their compressibility, shear strength, permeability, volumetric behaviour during shear including liquefaction potential, in-situ density and moisture content and specific gravity. The Cape Flats sands were found to be highly variable (with both inter- and intra-formation variation), with a wide range in many material properties, principally a function of soil texture, gradation and degree of cementation. The findings of this research may be used to form initial appreciation of the likely properties of the material and potential problem areas.
{"title":"Geotechnical properties of Cape Flats sands","authors":"N. Fouché, P. Day","doi":"10.17159/2309-8775/2022/v64no2a2","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64no2a2","url":null,"abstract":"The sand-covered coastal plain connecting the Cape Peninsula mountain chain to the southwestern Cape mainland is known as the Cape Flats. The whitish windblown sands covering this area of approximately 460 km2, referred to as the Quaternary sands of the Cape Flats, provide founding for the rapid and ongoing development in the area. A knowledge of the geotechnical properties and engineering behaviour of these sands is essential for design of suitable foundations for proposed structures and earthworks associated with such developments. By combining, analysing and interpreting the wealth of existing and available geotechnical information from previous and new soil investigations undertaken in the area, the Quaternary-aged sands of the Witzand, Springfontyn and Langebaan Formations from the Cape Flats were characterised in terms of their physical properties and engineering behaviour. The sands from the study area were classified based on their grading, Atterberg limits, maximum dry density and optimum moisture content, minimum dry density, California Bearing Ratio (CBR), erodibility and corrosivity, and characterised in terms of their compressibility, shear strength, permeability, volumetric behaviour during shear including liquefaction potential, in-situ density and moisture content and specific gravity. The Cape Flats sands were found to be highly variable (with both inter- and intra-formation variation), with a wide range in many material properties, principally a function of soil texture, gradation and degree of cementation. The findings of this research may be used to form initial appreciation of the likely properties of the material and potential problem areas.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45217643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a1
T. P. Mlilwana, E. Kearsley
Global population growth and rapid urbanisation have resulted in the rapid transformation of natural topographies that are now dominated by engineering materials and structures. It is widely recognised that economic development is largely attributable to infrastructure development. However, this development has come about with adverse consequences. In this paper, the effects of surface characteristics, climatic parameters and material properties on the thermal environment and near-surface heat islands in urban areas were investigated. An experiment was conducted in which simple concrete structures with varying surface characteristics were constructed and instrumented. The effect of solar absorptivity was clearly visible, with structures surfaced with low absorptivity materials exhibiting lower surface and effective temperatures. Following the experimental programme, numerical simulations of the simple concrete structures were performed using finite element modelling. The analyses showed that the thermal environment of concrete structures is sensitive to changes in solar absorptivity, climatic parameters, cross-sectional dimensions, and material properties. It was found that the use of low absorptivity or highly reflective surfacing and the selection of appropriate dimensions can be used to significantly reduce the temperatures of concrete infrastructure, including buildings and pavements, thereby providing an evidential basis for the use of low absorptivity surfacing materials to mitigate climate change in Southern Africa.
{"title":"Light-coloured concrete surfacing for urban heat-island mitigation in Southern Africa","authors":"T. P. Mlilwana, E. Kearsley","doi":"10.17159/2309-8775/2022/v64no2a1","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64no2a1","url":null,"abstract":"Global population growth and rapid urbanisation have resulted in the rapid transformation of natural topographies that are now dominated by engineering materials and structures. It is widely recognised that economic development is largely attributable to infrastructure development. However, this development has come about with adverse consequences. In this paper, the effects of surface characteristics, climatic parameters and material properties on the thermal environment and near-surface heat islands in urban areas were investigated. An experiment was conducted in which simple concrete structures with varying surface characteristics were constructed and instrumented. The effect of solar absorptivity was clearly visible, with structures surfaced with low absorptivity materials exhibiting lower surface and effective temperatures. Following the experimental programme, numerical simulations of the simple concrete structures were performed using finite element modelling. The analyses showed that the thermal environment of concrete structures is sensitive to changes in solar absorptivity, climatic parameters, cross-sectional dimensions, and material properties. It was found that the use of low absorptivity or highly reflective surfacing and the selection of appropriate dimensions can be used to significantly reduce the temperatures of concrete infrastructure, including buildings and pavements, thereby providing an evidential basis for the use of low absorptivity surfacing materials to mitigate climate change in Southern Africa.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49281415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a3
M. Otieno, K. Walter
Steel corrosion in reinforced concrete (RC) structures in the marine environment is a major concern for engineers and asset managers. This paper presents an assessment of the application of a deemed-to-satisfy durability design and specification approach on the newly constructed RC bridges on the Swakopmund-Walvis Bay Freeway upgrade in Namibia, with a desired service life of at least 100 years. The deemed-to-satisfy design and specification approach comprised a combination of South African recommendations for binder type, minimum binder content and w/b ratio, EN 206-1 recommendations for cover depth, and South African National Roads Agency Limited (SANRAL) durability index targets along with on-site concrete quality control guidelines on placement, compaction and curing. As-built concrete durability properties (i.e. water sorptivity, oxygen permeability and chloride conductivity) and cover depth were measured and used to check (using a Fickian-based service life model) if the deemed-to-satisfy specifications were adequate. The results showed that the as-built concrete durability properties surpassed the deemed-to-satisfy durability performance targets, while the on-site cover depth values showed significant inadequacies in some bridge elements. The service life estimations showed that the deemed-to-satisfy durability performance specifications were adequate. Considering the relatively high concrete quality achieved on site, it is clear that the 100-year service life could have been achieved more sustainably using a good balance of concrete quality and cover depth [e.g. a lower concrete quality (using less cement) or lesser coved depth] if a more rigorous performance-based durability design and specification approach had been used. Ultimately, the service life analyses using the as-built concrete model input parameters highlight not only the critical importance of both concrete quality and cover depth in achieving durable RC structures prone to steel corrosion, but also the inherent limitations of the deemed-to-satisfy durability design and specification approach.
{"title":"An assessment of a practical implementation of the deemed-to-satisfy durability design and specification approach in the Swakopmund-Walvis Bay Freeway upgrade project in Namibia","authors":"M. Otieno, K. Walter","doi":"10.17159/2309-8775/2022/v64no2a3","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64no2a3","url":null,"abstract":"Steel corrosion in reinforced concrete (RC) structures in the marine environment is a major concern for engineers and asset managers. This paper presents an assessment of the application of a deemed-to-satisfy durability design and specification approach on the newly constructed RC bridges on the Swakopmund-Walvis Bay Freeway upgrade in Namibia, with a desired service life of at least 100 years. The deemed-to-satisfy design and specification approach comprised a combination of South African recommendations for binder type, minimum binder content and w/b ratio, EN 206-1 recommendations for cover depth, and South African National Roads Agency Limited (SANRAL) durability index targets along with on-site concrete quality control guidelines on placement, compaction and curing. As-built concrete durability properties (i.e. water sorptivity, oxygen permeability and chloride conductivity) and cover depth were measured and used to check (using a Fickian-based service life model) if the deemed-to-satisfy specifications were adequate. The results showed that the as-built concrete durability properties surpassed the deemed-to-satisfy durability performance targets, while the on-site cover depth values showed significant inadequacies in some bridge elements. The service life estimations showed that the deemed-to-satisfy durability performance specifications were adequate. Considering the relatively high concrete quality achieved on site, it is clear that the 100-year service life could have been achieved more sustainably using a good balance of concrete quality and cover depth [e.g. a lower concrete quality (using less cement) or lesser coved depth] if a more rigorous performance-based durability design and specification approach had been used. Ultimately, the service life analyses using the as-built concrete model input parameters highlight not only the critical importance of both concrete quality and cover depth in achieving durable RC structures prone to steel corrosion, but also the inherent limitations of the deemed-to-satisfy durability design and specification approach.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45190297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a5
P. Luo, J. Liu
This paper proposes an innovative precast shear wall system built with precast concrete two-way hollow slabs (PCHS shear walls). In the joints of the precast panels of the PCHS shear walls, noncontact lap splices of rebars with vertical and horizontal holes are used to connect adjacent precast panels. These panels contribute to an automated assembly and facilitate pouring concrete in-situ. The mechanical behaviour of PCHS shear walls and the connection performance of vertical joints are examined through pseudo-static loading testing on one cast-in-situ concrete shear wall and four PCHS shear walls. Moreover, the influences of different parameters, including axial compression ratio, aspect ratio and the magnitude of horizontal distribution reinforcements, were analysed. It was found that the "strong bending and weak shear" requirement was achieved for all specimens. For the PCHS shear walls, the typical prominent diagonal cracks and brittle failure were prevented by the shear slippage at vertical joints and vertical cracks. And the vertical joint enabled the PCHS shear walls to exhibit stable load-bearing capacity with extensive deformations. In addition, the displacement ductility coefficient of all PCHS shear walls was over 5.0, and their ultimate drifts were over 1/100. The bearing capacity was improved with the increase of the axial compression ratio or with the decrease of the aspect ratio, but the deformation capacity was weakened.
{"title":"An experimental study of the mechanical behaviour of squat shear walls built with precast concrete two-way hollow slabs","authors":"P. Luo, J. Liu","doi":"10.17159/2309-8775/2022/v64no2a5","DOIUrl":"https://doi.org/10.17159/2309-8775/2022/v64no2a5","url":null,"abstract":"This paper proposes an innovative precast shear wall system built with precast concrete two-way hollow slabs (PCHS shear walls). In the joints of the precast panels of the PCHS shear walls, noncontact lap splices of rebars with vertical and horizontal holes are used to connect adjacent precast panels. These panels contribute to an automated assembly and facilitate pouring concrete in-situ. The mechanical behaviour of PCHS shear walls and the connection performance of vertical joints are examined through pseudo-static loading testing on one cast-in-situ concrete shear wall and four PCHS shear walls. Moreover, the influences of different parameters, including axial compression ratio, aspect ratio and the magnitude of horizontal distribution reinforcements, were analysed. It was found that the \"strong bending and weak shear\" requirement was achieved for all specimens. For the PCHS shear walls, the typical prominent diagonal cracks and brittle failure were prevented by the shear slippage at vertical joints and vertical cracks. And the vertical joint enabled the PCHS shear walls to exhibit stable load-bearing capacity with extensive deformations. In addition, the displacement ductility coefficient of all PCHS shear walls was over 5.0, and their ultimate drifts were over 1/100. The bearing capacity was improved with the increase of the axial compression ratio or with the decrease of the aspect ratio, but the deformation capacity was weakened.","PeriodicalId":54762,"journal":{"name":"Journal of the South African Institution of Civil Engineering","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2022-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45420543","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-05DOI: 10.17159/2309-8775/2022/v64no2a4
P. W. W. Visagie, T. Haas, G. P. V. van Zijl
Practicing engineers typically follow linear methods for seismic design and assessment, confining their approach to the requirements of SANS 10160-4 (SANS 2017). This generally leads to a conservative design, leaving little space to apply additional tools for design refinement. Soil-structure interaction has beneficial effects for most building structures under seismic action. However, incorporating soil-structure interaction in the analysis influences the fundamental period, damping and ductility, and will therefore influence the behaviour factor prescribed by design codes. The behaviour factor is necessary for linear methods (force-based methods) to predict the nonlinear behaviour of the structure. This investigation assessed the current behaviour factor for reinforced concrete walls in low- to medium-rise buildings, as prescribed by SANS 10160-4 (SANS 2017), when soil-structure interaction is incorporated in the analysis. The buildings were initially designed and detailed using linear methods, with the prescribed behaviour factor, and then tested using nonlinear methods that do not require the use of a behaviour factor.
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