Despite the recognition of the need for broad-based integrative
education that prepares students ... more Despite the recognition of the need for broad-based integrative education that prepares students for addressing complex problems in the real world, multi-disciplinary course offerings remain rare. The paper describes the development and offering of a multi-disciplinary graduate course covering earthquake loss assessment and mitigation ‘from source to society’. The course is built upon the comprehensive research, education, and outreach activities of the National Science Foundation-funded Mid-America Earthquake (MAE) Centre through the paradigm of consequence-based risk management (CRM). This is the first course of its kind in the field of earthquake engineering to expose students to the earthquake problem from source to society. The course was successfully offered at the University of Illinois at Urbana-Champaign, and will be offered at other universities. The CRM programme is a successful model for similar educational experiences. It opens new avenues in education of loss assessment and mitigation to meet the demands on the engineering profession by integration of engineering, social-economic science and information technology in a single multi-disciplinary course.
This paper investigates the effect of the horizontal and vertical components of ground motions (H... more This paper investigates the effect of the horizontal and vertical components of ground motions (HGM and VGM, respectively) on the seismic response of Reinforced Concrete (RC) buildings designed to modern capacity design principles and located in the vicinity of active faults. Fiber-based analytical models are used to monitor the global and local response of twelve reference structures, including verifying the response modification factor and tracing the member shear supply-demand response using a ductility- and axial force-sensitive shear strength approach. The simulation models are subjected to nearfield earthquake records with increasing severity up to collapse, including and excluding VGM. The results indicate that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of VGM. The fluctuation of axial forces in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has impact on shear capacity. The diverse range of buildings and performance criteria and large number of incremental dynamic analyses confirm the importance of including VGM in seismic design and assessment of contemporary RC buildings, and hence cast doubts on the reliability of pre-code structures located in the vicinity of active faults.
Investigating and planning for the expected damage that may hit the earthquake-prone areas in the... more Investigating and planning for the expected damage that may hit the earthquake-prone areas in the UAE should be undertaken in order to predict and mitigate earthquake losses. This paper discusses a framework for developing an essential driving engine in loss estimation systems, namely fragility relationships. Six reference structures, varying in height from 10 to 60 storeys, are selected due to the concentrated economic and human assets in this class of buildings. The reference structures are designed according to the building codes and construction practice adopted in this region. Inelastic fibre-based simulation models are developed for the buildings using a verified analysis platform, which enables monitoring the spread of yielding and cracking during the multi-step cyclic analysis. The ground motion uncertainty is accounted for using 20 input ground motions conforming to the latest understanding of the seismo-tectonic characteristics of the UAE. A large number of inelastic pushover and incremental dynamic collapse analyses are deployed for the reference structures to derive the fragility relationships. The study illustrates the significance of assessing the vulnerability of a population of high-rise buildings under the effect of various seismic scenarios and the need for expanding this study to cover other classes of structures in this region.
The multi-limit state seismic design and evaluation procedure allows structures to satisfy differ... more The multi-limit state seismic design and evaluation procedure allows structures to satisfy different performance criteria against different levels of seismic excitation. To achieve the simultaneous satisfaction of the multi-level design approach, it is essential to employ accurate analysis procedures which can be consistently applied to various levels of ground motions. In this study, several analytical evaluation procedures are compared via the application of the methods to two bridge structures. In the first application, a bridge considered typical of the inventory in the Central and Eastern United States is analyzed. Inelastic Response History Analysis (IRHA), two Capacity Spectrum Methods (CSMs), two Elastic Response History Analysis (ERHA) approaches with different stiffness approximation, and SDOF simulations are conducted. The second and more complex application, a 59-span irregular bridge crossing the Mississippi River is also analyzed in the elastic and inelastic ranges. Results from IRHA and simplified analysis procedures are compared to assess their applicability and limitations. It is concluded that the approximate methods have limited applicability, which depends on several parameters including intensity of ground motions and characteristics of bridge structures. The importance of inelastic and dynamic analysis in seismic assessment is emphasized, while cases where the simplified procedures yield acceptable response are presented.
Owing to the simplicity of inelastic static pushover analysis compared to inelastic dynamic analy... more Owing to the simplicity of inelastic static pushover analysis compared to inelastic dynamic analysis, the study of this technique has been the subject of many investigations in recent years. In this paper, the validity and the applicability of this technique are assessed by comparison with 'dynamic pushover' idealised envelopes obtained from incremental dynamic collapse analysis. This is undertaken using natural and artificial earthquake records imposed on 12 RC buildings of different characteristics. This involves successive scaling and application of each accelerogram followed by assessment of the maximum response, up to the achievement of the structural collapse. The results of over one hundred inelastic dynamic analyses using a detailed 2D modelling approach for each of the twelve RC buildings have been utilised to develop the dynamic pushover envelopes and compare these with the static pushover results with different load patterns. Good correlation is obtained between the calculated idealised envelopes of the dynamic analyses and static pushover results for a defined class of structure. Where discrepancies were observed, extensive investigations based on Fourier amplitude analysis of the response were undertaken and conservative assumptions were recommended.
A comprehensive study is undertaken to assess and calibrate the force reduction factors (R) adopt... more A comprehensive study is undertaken to assess and calibrate the force reduction factors (R) adopted in modern seismic codes. Refined expressions are employed to calculate the R factors “supply” for 12 buildings of various characteristics represent a wide range of medium-rise RC buildings. The “supply” values are then compared with the “design” and “demand” recommended in the literature. A comprehensive range of response criteria at the member and storey levels, including shear as a failure criterion, alongside a detailed modelling approach and an extensively verified analytical tool are utilised. A rigorous technique is employed to evaluate R factors, including inelastic pushover and incremental dynamic collapse analyses employing eight natural and artificial records. In the light of the information obtained from more than 1500 inelastic analyses, it is concluded that including shear and vertical motion in assessment and calculations of R factors is necessary. Force reduction factors adopted by the design code (Eurocode 8) are over-conservative and can be safely increased, particularly for regular frame structures designed to lower PGA and higher ductility levels.
The paper presents a detailed seismic performance assessment of a complex bridge designed as a re... more The paper presents a detailed seismic performance assessment of a complex bridge designed as a reference application of modern codes for the Federal Highway Administration. The assessment utilizes state-of-the-art assessment tools and response metrics. The impact of design assumptions on the capacity estimates and demand predictions of the multispan curved bridge is investigated. The level of attention to detail is significantly higher than can be achieved in a mass parametric study of a population of bridges. The objective of in-depth assessment is achieved through investigation of the bridge using two models. The first represents the bridge as designed ͑including features assumed in the design process͒ while the second represents the bridge as built ͑actual expected characteristics͒. Three-dimensional detailed dynamic response simulations of the investigated bridge, including soil-structure interaction, are undertaken. The behavior of the as-designed bridge is investigated using two different analytical platforms for elastic and inelastic analysis, for the purposes of verification. A third idealization is adopted to investigate the as-built bridge's behavior by realistically modeling bridge bearings, structural gaps, and materials. A comprehensive list of local and global, action and deformation performance indicators, including bearing slippage and inter-segment collision, are selected to monitor the response to earthquake ground motion. The comparative study has indicated that the lateral capacity and dynamic characteristics of the as-designed bridge are significantly different from the as-built bridge's behavior. The potential of pushover analysis in identifying structural deficiencies, estimating capacities, and providing insight into the pertinent limit state criteria is demonstrated. Comparison of seismic demand with available capacity shows that seemingly conservative design assumptions, such as ignoring friction at the bearings, may lead to an erroneous and potentially nonconservative response expectation. The recommendations assist design engineers seeking to achieve realistic predictions of seismic behavior and thus contribute to uncertainty reduction in the ensuing design.
This paper investigates the implications of ground motion spatial variability on the seismic resp... more This paper investigates the implications of ground motion spatial variability on the seismic response of an extended highway bridge. An existing 59-span, 2,164-meter bridge with several bearing types and irregularity features was selected as a reference structure. The bridge is located in the New Madrid Seismic Zone and supported on thick layers of soil deposits. Site-specific bedrock input ground motions were selected based on a refined probabilistic seismic hazard analysis of the bridge site. Wave passage and ground motion incoherency effects were accounted for after propagating the bedrock records to the ground surface. The results obtained from inelastic response-history analyses confirm the significant impact of wave passage and ground motion incoherency on the seismic behavior of the bridge. The amplification in seismic demands exceeds 150%, whereas the maximum suppression of these demands is less than 50%. The irregular and unpredictable changes in structural response owing to asynchronous earthquake records necessitate in-depth seismic assessment of major highway bridges with advanced modeling techniques to realistically capture their complex seismic response.
Earthquake Engineering and Engineering Vibration, 2011
To verify the seismic design response factors of high-rise buildings, five reference structures, ... more To verify the seismic design response factors of high-rise buildings, five reference structures, varying in height from 20- to 60-stories, were selected and designed according to modern design codes to represent a wide range of concrete wall structures. Verified fiber-based analytical models for inelastic simulation were developed, considering the geometric nonlinearity and material inelasticity of the structural members. The ground motion uncertainty was accounted for by employing 20 earthquake records representing two seismic scenarios, consistent with the latest understanding of the tectonic setting and seismicity of the selected reference region (UAE). A large number of Inelastic Pushover Analyses (IPAs) and Incremental Dynamic Collapse Analyses (IDCAs) were deployed for the reference structures to estimate the seismic design response factors. It is concluded that the factors adopted by the design code are adequately conservative. The results of this systematic assessment of seismic design response factors apply to a wide variety of contemporary concrete wall buildings with various characteristics.
Starting from a typical bridge from the inventory of FHWA concept designs, comparative analyses a... more Starting from a typical bridge from the inventory of FHWA concept designs, comparative analyses are conducted to evaluate the influence of friction bearing models on the dynamic characteristics and predicted seismic response of multi-span bridges. Refined 3-dimensional idealizations of the selected nine-span bridge were assembled for assessment using two analysis platforms. Comprehensive analyses were conducted to estimate the dynamic characteristics and demands of the bridge components in the longitudinal and transverse directions. Contrary to the design assumption, it is concluded that the behavior is significantly and fundamentally affected by taking account of friction at bearings, especially with regard to forces. The study confirms that neglecting friction in design is non-conservative and may compromise safety of the structure.
In the vicinity of the source of moderate-to-strong earthquakes, the ratio of peak vertical to ho... more In the vicinity of the source of moderate-to-strong earthquakes, the ratio of peak vertical to horizontal acceleration (V/H) often exceeds the values around 2/3 rd adopted in design codes. The difference in frequency content between the vertical and horizontal ground motions (VGM and HGM, respectively), when coupled with difference between the vertical and horizontal dynamic characteristics of structures, cast doubt regarding the adequacy of the simplified approach adopted in seismic design codes. There are also increasing field evidences confirming the significance of VGM. These evidences were even observed in regions where state-of-the-art in earthquake design practice is applied, such as Japan and the USA. The objective of this paper is to investigate the effect of VGM on seismic response and force reduction factors 'supply' of multi-storey RC buildings located in the vicinity of active faults and designed to modern seismic codes employing capacity design principles. A comprehensive set of local and global response parameters is selected to assess the building response under multi-axial earthquake loading (HGM and VGM). These include assessment of the shear supply-demand response of structural members using a realistic ductility-and axial forcesensitive shear strength approach. Near-field earthquake records with moderate-to-high V/H ratios are selected to provide realistic conclusions regarding the effect of VGM. The wide range of buildings and performance criteria selected and the state-of-the-art modeling approaches adopted render the results of this study indicative of response trends. It is concluded that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of vertical motion. The fluctuation of axial force in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has considerable impact on the shear capacity. Although the investigated buildings are designed and detailed according to modern seismic codes, the importance of including VGM in seismic design and assessment of RC buildings in the vicinity of active faults is emphasized.
A comprehensive study carried out to assess the seismic response of a 59-span bridge using a refi... more A comprehensive study carried out to assess the seismic response of a 59-span bridge using a refined inelastic modeling approach and considering Soil-Structure Interaction (SSI) is summarized in this paper. The focus is on describing the methodology adopted to idealize the bridge and its foundation system, while only highlights from the extensive elastic and inelastic analyses are presented. The bridge represents a typical case of vulnerable complex bridges since it was built in the early seventies with minimal seismic design requirements at a distance of about 5 km from a major fault. The SSI analysis is significant in this study due to the length of the bridge, the massive and stiff foundation, and the relatively soft deep soil of the site. A series of three-dimensional dynamic response simulations of the entire bridge are conducted using several analysis tools to verify the developed analytical models. The performance-based assessment study employs 144 site-specific input ground motions representing three seismic scenarios, corresponding to 500, 1000 and 2500 years return periods, to identify areas of vulnerability in the 2164-meter bridge at various hazard levels. It is concluded that the seismic response of the bridge at the 500 years ground motions does not meet today's standards, while the demands under the effect of the 1000 years ground motions almost exceed the capacity of most bridge components. The demands significantly increase under the effect of the 2500 years earthquake scenario and considerably exceed the collapse limit states. The results clearly reflect the benefit of retrofitting different bridge components to mitigate the anticipated seismic risk. The presented assessment study contributes to improve public safety by exploiting the most recent research outcomes in predicting the seismic response of complex highway bridges, which are essential for developing reliable and cost-effective retrofit strategies.
Shear failure of RC structures signifies rapid strength degradation and significant loss of energ... more Shear failure of RC structures signifies rapid strength degradation and significant loss of energy dissipation capacity. It is thus necessary to avoid this failure mode by insuring that the shear supply exceeds the capacity corresponding to the maximum realistic flexural strength. A realistic and versatile approach is proposed in the current study and implemented in a general nonlinear dynamic analysis program to allow for the prediction of shear failure in structural member. The shear demand-supply response is monitored through employing two shear strength approaches. The first is based on extensive experimental results and has proven to be effective in representing the reduction of shear supply with the degradation in concrete strength. A design code shear strength model is also selected for comparison after eliminating the safety factors used by the code. The analytical models are implemented in a time-step fashion to allow for shear-axial interaction and to account for the instantaneous ductility demand imposed during the analysis. The investigated structures were realistically designed and detailed to different design ground accelerations and capacity design requirements to represent a wide range of contemporary buildings with variations in longitudinal (flexure) and transverse (shear and confinement) reinforcement. A series of inelastic response history analyses is conducted using a set of earthquake records scaled to increasing intensities up to collapse. The significance of including shear as a failure criterion in seismic assessment is confirmed in this study. Variations of axial forces lead to high fluctuation in shear supply and decrease the contribution of the concrete compression zone to shear resistance. The improved response of structural members designed to the modern seismic provisions is confirmed. Shear failure may be the controlling limit state in buildings designed for low-to-medium ductility capacity. This suggests improvements in the design provisions, particularly those related to beam critical regions.
Fragility analyses are conducted in this study to evaluate the relative seismic safety margins of... more Fragility analyses are conducted in this study to evaluate the relative seismic safety margins of seismic code-designed multi-story reinforced concrete (RC) buildings with varying input motion intensity, ductility level and configuration. Structural variations are accounted for by using twelve buildings [13] with diverse structural systems, heights and ductile detailing. The design peak ground acceleration (PGA) is also varied. The reference structures also include regular and irregular buildings in order to cover a wide spectrum of contemporary mid-rise buildings. Incremental dynamic analyses (IDAs) are deployed using the twelve inelastic fiber-based simulation models of the reference structures and sixty natural ground motions recorded on different soil conditions with a wide range of spectral amplifications. The regression analyses of the selected response quantities show that the soil condition has a marginal effect on the demand-ground motion intensity relationships when adopting spectral acceleration to characterize the ground shaking intensity. The damage state probabilities of wall-frame structures designed to high PGA and ductility levels do not satisfactorily achieve the most favorable safety objectives. Fragilities are reduced by decreasing the design PGA due to the higher contribution of gravity loads to the details of the building design. Using extensive results from twelve buildings subjected to sixty ground motions, a relationship is proposed to enable the quantifying of the Life Safety limit state probabilities of codecompliant mid-rise RC buildings.
Despite the recognition of the need for broad-based integrative
education that prepares students ... more Despite the recognition of the need for broad-based integrative education that prepares students for addressing complex problems in the real world, multi-disciplinary course offerings remain rare. The paper describes the development and offering of a multi-disciplinary graduate course covering earthquake loss assessment and mitigation ‘from source to society’. The course is built upon the comprehensive research, education, and outreach activities of the National Science Foundation-funded Mid-America Earthquake (MAE) Centre through the paradigm of consequence-based risk management (CRM). This is the first course of its kind in the field of earthquake engineering to expose students to the earthquake problem from source to society. The course was successfully offered at the University of Illinois at Urbana-Champaign, and will be offered at other universities. The CRM programme is a successful model for similar educational experiences. It opens new avenues in education of loss assessment and mitigation to meet the demands on the engineering profession by integration of engineering, social-economic science and information technology in a single multi-disciplinary course.
This paper investigates the effect of the horizontal and vertical components of ground motions (H... more This paper investigates the effect of the horizontal and vertical components of ground motions (HGM and VGM, respectively) on the seismic response of Reinforced Concrete (RC) buildings designed to modern capacity design principles and located in the vicinity of active faults. Fiber-based analytical models are used to monitor the global and local response of twelve reference structures, including verifying the response modification factor and tracing the member shear supply-demand response using a ductility- and axial force-sensitive shear strength approach. The simulation models are subjected to nearfield earthquake records with increasing severity up to collapse, including and excluding VGM. The results indicate that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of VGM. The fluctuation of axial forces in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has impact on shear capacity. The diverse range of buildings and performance criteria and large number of incremental dynamic analyses confirm the importance of including VGM in seismic design and assessment of contemporary RC buildings, and hence cast doubts on the reliability of pre-code structures located in the vicinity of active faults.
Investigating and planning for the expected damage that may hit the earthquake-prone areas in the... more Investigating and planning for the expected damage that may hit the earthquake-prone areas in the UAE should be undertaken in order to predict and mitigate earthquake losses. This paper discusses a framework for developing an essential driving engine in loss estimation systems, namely fragility relationships. Six reference structures, varying in height from 10 to 60 storeys, are selected due to the concentrated economic and human assets in this class of buildings. The reference structures are designed according to the building codes and construction practice adopted in this region. Inelastic fibre-based simulation models are developed for the buildings using a verified analysis platform, which enables monitoring the spread of yielding and cracking during the multi-step cyclic analysis. The ground motion uncertainty is accounted for using 20 input ground motions conforming to the latest understanding of the seismo-tectonic characteristics of the UAE. A large number of inelastic pushover and incremental dynamic collapse analyses are deployed for the reference structures to derive the fragility relationships. The study illustrates the significance of assessing the vulnerability of a population of high-rise buildings under the effect of various seismic scenarios and the need for expanding this study to cover other classes of structures in this region.
The multi-limit state seismic design and evaluation procedure allows structures to satisfy differ... more The multi-limit state seismic design and evaluation procedure allows structures to satisfy different performance criteria against different levels of seismic excitation. To achieve the simultaneous satisfaction of the multi-level design approach, it is essential to employ accurate analysis procedures which can be consistently applied to various levels of ground motions. In this study, several analytical evaluation procedures are compared via the application of the methods to two bridge structures. In the first application, a bridge considered typical of the inventory in the Central and Eastern United States is analyzed. Inelastic Response History Analysis (IRHA), two Capacity Spectrum Methods (CSMs), two Elastic Response History Analysis (ERHA) approaches with different stiffness approximation, and SDOF simulations are conducted. The second and more complex application, a 59-span irregular bridge crossing the Mississippi River is also analyzed in the elastic and inelastic ranges. Results from IRHA and simplified analysis procedures are compared to assess their applicability and limitations. It is concluded that the approximate methods have limited applicability, which depends on several parameters including intensity of ground motions and characteristics of bridge structures. The importance of inelastic and dynamic analysis in seismic assessment is emphasized, while cases where the simplified procedures yield acceptable response are presented.
Owing to the simplicity of inelastic static pushover analysis compared to inelastic dynamic analy... more Owing to the simplicity of inelastic static pushover analysis compared to inelastic dynamic analysis, the study of this technique has been the subject of many investigations in recent years. In this paper, the validity and the applicability of this technique are assessed by comparison with 'dynamic pushover' idealised envelopes obtained from incremental dynamic collapse analysis. This is undertaken using natural and artificial earthquake records imposed on 12 RC buildings of different characteristics. This involves successive scaling and application of each accelerogram followed by assessment of the maximum response, up to the achievement of the structural collapse. The results of over one hundred inelastic dynamic analyses using a detailed 2D modelling approach for each of the twelve RC buildings have been utilised to develop the dynamic pushover envelopes and compare these with the static pushover results with different load patterns. Good correlation is obtained between the calculated idealised envelopes of the dynamic analyses and static pushover results for a defined class of structure. Where discrepancies were observed, extensive investigations based on Fourier amplitude analysis of the response were undertaken and conservative assumptions were recommended.
A comprehensive study is undertaken to assess and calibrate the force reduction factors (R) adopt... more A comprehensive study is undertaken to assess and calibrate the force reduction factors (R) adopted in modern seismic codes. Refined expressions are employed to calculate the R factors “supply” for 12 buildings of various characteristics represent a wide range of medium-rise RC buildings. The “supply” values are then compared with the “design” and “demand” recommended in the literature. A comprehensive range of response criteria at the member and storey levels, including shear as a failure criterion, alongside a detailed modelling approach and an extensively verified analytical tool are utilised. A rigorous technique is employed to evaluate R factors, including inelastic pushover and incremental dynamic collapse analyses employing eight natural and artificial records. In the light of the information obtained from more than 1500 inelastic analyses, it is concluded that including shear and vertical motion in assessment and calculations of R factors is necessary. Force reduction factors adopted by the design code (Eurocode 8) are over-conservative and can be safely increased, particularly for regular frame structures designed to lower PGA and higher ductility levels.
The paper presents a detailed seismic performance assessment of a complex bridge designed as a re... more The paper presents a detailed seismic performance assessment of a complex bridge designed as a reference application of modern codes for the Federal Highway Administration. The assessment utilizes state-of-the-art assessment tools and response metrics. The impact of design assumptions on the capacity estimates and demand predictions of the multispan curved bridge is investigated. The level of attention to detail is significantly higher than can be achieved in a mass parametric study of a population of bridges. The objective of in-depth assessment is achieved through investigation of the bridge using two models. The first represents the bridge as designed ͑including features assumed in the design process͒ while the second represents the bridge as built ͑actual expected characteristics͒. Three-dimensional detailed dynamic response simulations of the investigated bridge, including soil-structure interaction, are undertaken. The behavior of the as-designed bridge is investigated using two different analytical platforms for elastic and inelastic analysis, for the purposes of verification. A third idealization is adopted to investigate the as-built bridge's behavior by realistically modeling bridge bearings, structural gaps, and materials. A comprehensive list of local and global, action and deformation performance indicators, including bearing slippage and inter-segment collision, are selected to monitor the response to earthquake ground motion. The comparative study has indicated that the lateral capacity and dynamic characteristics of the as-designed bridge are significantly different from the as-built bridge's behavior. The potential of pushover analysis in identifying structural deficiencies, estimating capacities, and providing insight into the pertinent limit state criteria is demonstrated. Comparison of seismic demand with available capacity shows that seemingly conservative design assumptions, such as ignoring friction at the bearings, may lead to an erroneous and potentially nonconservative response expectation. The recommendations assist design engineers seeking to achieve realistic predictions of seismic behavior and thus contribute to uncertainty reduction in the ensuing design.
This paper investigates the implications of ground motion spatial variability on the seismic resp... more This paper investigates the implications of ground motion spatial variability on the seismic response of an extended highway bridge. An existing 59-span, 2,164-meter bridge with several bearing types and irregularity features was selected as a reference structure. The bridge is located in the New Madrid Seismic Zone and supported on thick layers of soil deposits. Site-specific bedrock input ground motions were selected based on a refined probabilistic seismic hazard analysis of the bridge site. Wave passage and ground motion incoherency effects were accounted for after propagating the bedrock records to the ground surface. The results obtained from inelastic response-history analyses confirm the significant impact of wave passage and ground motion incoherency on the seismic behavior of the bridge. The amplification in seismic demands exceeds 150%, whereas the maximum suppression of these demands is less than 50%. The irregular and unpredictable changes in structural response owing to asynchronous earthquake records necessitate in-depth seismic assessment of major highway bridges with advanced modeling techniques to realistically capture their complex seismic response.
Earthquake Engineering and Engineering Vibration, 2011
To verify the seismic design response factors of high-rise buildings, five reference structures, ... more To verify the seismic design response factors of high-rise buildings, five reference structures, varying in height from 20- to 60-stories, were selected and designed according to modern design codes to represent a wide range of concrete wall structures. Verified fiber-based analytical models for inelastic simulation were developed, considering the geometric nonlinearity and material inelasticity of the structural members. The ground motion uncertainty was accounted for by employing 20 earthquake records representing two seismic scenarios, consistent with the latest understanding of the tectonic setting and seismicity of the selected reference region (UAE). A large number of Inelastic Pushover Analyses (IPAs) and Incremental Dynamic Collapse Analyses (IDCAs) were deployed for the reference structures to estimate the seismic design response factors. It is concluded that the factors adopted by the design code are adequately conservative. The results of this systematic assessment of seismic design response factors apply to a wide variety of contemporary concrete wall buildings with various characteristics.
Starting from a typical bridge from the inventory of FHWA concept designs, comparative analyses a... more Starting from a typical bridge from the inventory of FHWA concept designs, comparative analyses are conducted to evaluate the influence of friction bearing models on the dynamic characteristics and predicted seismic response of multi-span bridges. Refined 3-dimensional idealizations of the selected nine-span bridge were assembled for assessment using two analysis platforms. Comprehensive analyses were conducted to estimate the dynamic characteristics and demands of the bridge components in the longitudinal and transverse directions. Contrary to the design assumption, it is concluded that the behavior is significantly and fundamentally affected by taking account of friction at bearings, especially with regard to forces. The study confirms that neglecting friction in design is non-conservative and may compromise safety of the structure.
In the vicinity of the source of moderate-to-strong earthquakes, the ratio of peak vertical to ho... more In the vicinity of the source of moderate-to-strong earthquakes, the ratio of peak vertical to horizontal acceleration (V/H) often exceeds the values around 2/3 rd adopted in design codes. The difference in frequency content between the vertical and horizontal ground motions (VGM and HGM, respectively), when coupled with difference between the vertical and horizontal dynamic characteristics of structures, cast doubt regarding the adequacy of the simplified approach adopted in seismic design codes. There are also increasing field evidences confirming the significance of VGM. These evidences were even observed in regions where state-of-the-art in earthquake design practice is applied, such as Japan and the USA. The objective of this paper is to investigate the effect of VGM on seismic response and force reduction factors 'supply' of multi-storey RC buildings located in the vicinity of active faults and designed to modern seismic codes employing capacity design principles. A comprehensive set of local and global response parameters is selected to assess the building response under multi-axial earthquake loading (HGM and VGM). These include assessment of the shear supply-demand response of structural members using a realistic ductility-and axial forcesensitive shear strength approach. Near-field earthquake records with moderate-to-high V/H ratios are selected to provide realistic conclusions regarding the effect of VGM. The wide range of buildings and performance criteria selected and the state-of-the-art modeling approaches adopted render the results of this study indicative of response trends. It is concluded that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of vertical motion. The fluctuation of axial force in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has considerable impact on the shear capacity. Although the investigated buildings are designed and detailed according to modern seismic codes, the importance of including VGM in seismic design and assessment of RC buildings in the vicinity of active faults is emphasized.
A comprehensive study carried out to assess the seismic response of a 59-span bridge using a refi... more A comprehensive study carried out to assess the seismic response of a 59-span bridge using a refined inelastic modeling approach and considering Soil-Structure Interaction (SSI) is summarized in this paper. The focus is on describing the methodology adopted to idealize the bridge and its foundation system, while only highlights from the extensive elastic and inelastic analyses are presented. The bridge represents a typical case of vulnerable complex bridges since it was built in the early seventies with minimal seismic design requirements at a distance of about 5 km from a major fault. The SSI analysis is significant in this study due to the length of the bridge, the massive and stiff foundation, and the relatively soft deep soil of the site. A series of three-dimensional dynamic response simulations of the entire bridge are conducted using several analysis tools to verify the developed analytical models. The performance-based assessment study employs 144 site-specific input ground motions representing three seismic scenarios, corresponding to 500, 1000 and 2500 years return periods, to identify areas of vulnerability in the 2164-meter bridge at various hazard levels. It is concluded that the seismic response of the bridge at the 500 years ground motions does not meet today's standards, while the demands under the effect of the 1000 years ground motions almost exceed the capacity of most bridge components. The demands significantly increase under the effect of the 2500 years earthquake scenario and considerably exceed the collapse limit states. The results clearly reflect the benefit of retrofitting different bridge components to mitigate the anticipated seismic risk. The presented assessment study contributes to improve public safety by exploiting the most recent research outcomes in predicting the seismic response of complex highway bridges, which are essential for developing reliable and cost-effective retrofit strategies.
Shear failure of RC structures signifies rapid strength degradation and significant loss of energ... more Shear failure of RC structures signifies rapid strength degradation and significant loss of energy dissipation capacity. It is thus necessary to avoid this failure mode by insuring that the shear supply exceeds the capacity corresponding to the maximum realistic flexural strength. A realistic and versatile approach is proposed in the current study and implemented in a general nonlinear dynamic analysis program to allow for the prediction of shear failure in structural member. The shear demand-supply response is monitored through employing two shear strength approaches. The first is based on extensive experimental results and has proven to be effective in representing the reduction of shear supply with the degradation in concrete strength. A design code shear strength model is also selected for comparison after eliminating the safety factors used by the code. The analytical models are implemented in a time-step fashion to allow for shear-axial interaction and to account for the instantaneous ductility demand imposed during the analysis. The investigated structures were realistically designed and detailed to different design ground accelerations and capacity design requirements to represent a wide range of contemporary buildings with variations in longitudinal (flexure) and transverse (shear and confinement) reinforcement. A series of inelastic response history analyses is conducted using a set of earthquake records scaled to increasing intensities up to collapse. The significance of including shear as a failure criterion in seismic assessment is confirmed in this study. Variations of axial forces lead to high fluctuation in shear supply and decrease the contribution of the concrete compression zone to shear resistance. The improved response of structural members designed to the modern seismic provisions is confirmed. Shear failure may be the controlling limit state in buildings designed for low-to-medium ductility capacity. This suggests improvements in the design provisions, particularly those related to beam critical regions.
Fragility analyses are conducted in this study to evaluate the relative seismic safety margins of... more Fragility analyses are conducted in this study to evaluate the relative seismic safety margins of seismic code-designed multi-story reinforced concrete (RC) buildings with varying input motion intensity, ductility level and configuration. Structural variations are accounted for by using twelve buildings [13] with diverse structural systems, heights and ductile detailing. The design peak ground acceleration (PGA) is also varied. The reference structures also include regular and irregular buildings in order to cover a wide spectrum of contemporary mid-rise buildings. Incremental dynamic analyses (IDAs) are deployed using the twelve inelastic fiber-based simulation models of the reference structures and sixty natural ground motions recorded on different soil conditions with a wide range of spectral amplifications. The regression analyses of the selected response quantities show that the soil condition has a marginal effect on the demand-ground motion intensity relationships when adopting spectral acceleration to characterize the ground shaking intensity. The damage state probabilities of wall-frame structures designed to high PGA and ductility levels do not satisfactorily achieve the most favorable safety objectives. Fragilities are reduced by decreasing the design PGA due to the higher contribution of gravity loads to the details of the building design. Using extensive results from twelve buildings subjected to sixty ground motions, a relationship is proposed to enable the quantifying of the Life Safety limit state probabilities of codecompliant mid-rise RC buildings.
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Papers by Aman Mwafy
education that prepares students for addressing complex problems in the real world, multi-disciplinary course offerings remain rare. The paper describes the development and offering of a multi-disciplinary graduate course covering earthquake loss assessment and mitigation ‘from source to society’. The course is built upon the comprehensive research, education, and outreach activities of the National Science Foundation-funded Mid-America Earthquake (MAE) Centre through the paradigm of consequence-based risk management (CRM). This is the first course of its kind in the field of earthquake engineering to expose students to the earthquake problem from source to society. The course
was successfully offered at the University of Illinois at Urbana-Champaign, and will be offered at other universities. The CRM programme is a successful model for similar educational experiences. It opens new avenues in education of loss assessment and mitigation to meet the demands on the engineering profession by integration of engineering, social-economic science and information technology in a single multi-disciplinary course.
earthquake records with increasing severity up to collapse, including and excluding VGM. The results indicate that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of VGM. The fluctuation of axial forces in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has impact on shear capacity. The diverse range of buildings and performance criteria and large number of incremental dynamic analyses confirm the importance of including VGM in seismic design and assessment of contemporary RC buildings, and hence cast doubts
on the reliability of pre-code structures located in the vicinity of active faults.
reference structures, varying in height from 10 to 60 storeys, are selected due to the concentrated economic
and human assets in this class of buildings. The reference structures are designed according to the building codes and construction practice adopted in this region. Inelastic fibre-based simulation models are developed for the buildings using a verified analysis platform, which enables monitoring the spread of yielding and cracking during the multi-step cyclic analysis. The ground motion uncertainty is accounted for using 20 input ground motions conforming to the latest understanding of the seismo-tectonic characteristics of the UAE. A large number of inelastic pushover and incremental dynamic collapse analyses are deployed for the reference structures to derive the fragility relationships. The study illustrates the significance of assessing the vulnerability of a population of high-rise buildings under the effect of various seismic scenarios and the need for expanding this study to cover other classes of structures in this region.
education that prepares students for addressing complex problems in the real world, multi-disciplinary course offerings remain rare. The paper describes the development and offering of a multi-disciplinary graduate course covering earthquake loss assessment and mitigation ‘from source to society’. The course is built upon the comprehensive research, education, and outreach activities of the National Science Foundation-funded Mid-America Earthquake (MAE) Centre through the paradigm of consequence-based risk management (CRM). This is the first course of its kind in the field of earthquake engineering to expose students to the earthquake problem from source to society. The course
was successfully offered at the University of Illinois at Urbana-Champaign, and will be offered at other universities. The CRM programme is a successful model for similar educational experiences. It opens new avenues in education of loss assessment and mitigation to meet the demands on the engineering profession by integration of engineering, social-economic science and information technology in a single multi-disciplinary course.
earthquake records with increasing severity up to collapse, including and excluding VGM. The results indicate that the lower the contribution of horizontal seismic forces to the seismic response, the higher is the significance of VGM. The fluctuation of axial forces in vertical structural members significantly increases when including VGM. This not only has direct consequences on tension and compression response but also has impact on shear capacity. The diverse range of buildings and performance criteria and large number of incremental dynamic analyses confirm the importance of including VGM in seismic design and assessment of contemporary RC buildings, and hence cast doubts
on the reliability of pre-code structures located in the vicinity of active faults.
reference structures, varying in height from 10 to 60 storeys, are selected due to the concentrated economic
and human assets in this class of buildings. The reference structures are designed according to the building codes and construction practice adopted in this region. Inelastic fibre-based simulation models are developed for the buildings using a verified analysis platform, which enables monitoring the spread of yielding and cracking during the multi-step cyclic analysis. The ground motion uncertainty is accounted for using 20 input ground motions conforming to the latest understanding of the seismo-tectonic characteristics of the UAE. A large number of inelastic pushover and incremental dynamic collapse analyses are deployed for the reference structures to derive the fragility relationships. The study illustrates the significance of assessing the vulnerability of a population of high-rise buildings under the effect of various seismic scenarios and the need for expanding this study to cover other classes of structures in this region.