Earthquake Engineering Publications are listed below. They cover modeling aspects for engineers and researchers as well as new technologies including Modular Steel Structures and Self-Centering Structures. You can also check our Engineering Tools, and/or submit your engineering inquiries.
Xu C, Nehdi ML, Youssef MA, Wang T, Zhang LV, 2021, “Seismic Performance of RC Beam-Column Edge Joints Reinforced with Austenite Stainless Steel”, Engineering Structures, 232: 111824.
Using stainless steel (SS) reinforcement can mitigate colossal corrosion damage inflicted to reinforced concrete (RC) structures worldwide. However, there is still dearth of studies on the seismic behavior of SS-RC structures. Hence, quasi-static tests were carried out in this study to explore the seismic performance of three RC frame edge joint specimens reinforced with SS having strength grade of 500 and one control RC specimen made with grade 400 normal steel. RC edge frame joints reinforced with ordinary steel and SS exhibited similar bending-shear failure patterns at the beam root. The load bearing capacity of the SS-RC edge fame joint specimens was greater than that of the control ordinary steel specimen. SS-RC specimens BJD-1, BJD-2 and BJD-3 had 66.7%, 33.3% and 25% higher cracking load capacity than that of the control specimen BDJ-4, respectively. The yield load increased by 54.5%, 42.3% and 50.4%; while the ultimate load increased by 22.3%, 35.2% and 16.8%, respectively. The yield and ultimate displacements of the specimens were both larger, while the displacement ductility coefficient was smaller, than that of the control specimen. In addition, the energy dissipation and equivalent viscous damping coefficients of the SS reinforced specimens BJD-1, BJD-2 and BJD-3 in both the cracking and yield stages were all greater than that of the control specimen BDJ-4 but were slightly lower in the limit stage. Generally, SS-RC specimens met design code ductility requirements under earthquake loading, with adequate plastic deformation. A constitutive relationship for SS rebar was proposed in this study and used to conduct finite element simulations of the tested specimens. Good correlation between simulation and experimental results was observed. Thus, a parametric study was conducted to numerically investigate the influence of the axial compression, longitudinal and hoop reinforcement ratios on the seismic behavior of SS-RC joints. The findings could provide insight and guidance for future design provisions of concrete structures reinforced with stainless steel.
Youssef, M.A., Meshaly, M.E., Elansary, A., 2017, “Ductile Corrosion-Free GFRP-Stainless Steel Reinforced Concrete Elements”, Composite Structures, 182:124-131.
Corrosion of steel rebars is known to cause deterioration of concrete structures that can lead to catastrophic failures. To mitigate this problem, steel rebars can be replaced with Glass Fiber-Reinforced Polymer (GFRP) rebars. However, the lack of ductility of GFRP-reinforced elements has prevented their use in many structural applications, especially in seismic areas. Stainless Steel (SS) rebars are corrosion resistant and have adequate energy absorption and ductility. However, they are much more expensive than steel rebars. This paper proposes the combined use of SS and GFRP rebars to achieve ductile and corrosion-free elements. The first challenge for such a proposal relates to designing SS-GFRP reinforced concrete frame with adequate lateral performance in terms of initial stiffness, ductility, and strength. Design equations, which are based on a comprehensive parametric study, are developed to allow designing such a frame. A six-storey concrete frame is then designed using the proposed equations and its lateral performance is examined using pushover analysis.
Sultana, P., Youssef M.A., 2016, “Prediction of local seismic damage in steel moment resisting frames”, Journal of Constructional Steel Research, 122: 122-137.
Steel moment resisting frames (SMRFs) are widely utilized as a lateral load resisting system. Their seismic performance is usually assessed by examining the maximum value of inter-storey drift (MID) of all floors. The accuracy of such assessment is debatable given the wide spread of values of MID at collapse that exist in the literature. In this study, a simplified method to define the failure inter-storey drift for each floor of a SMRF is proposed. The method was validated with the experimental and analytical studies by other researchers. Three- and ten-storey SMRFs were considered to further validate the proposed method. The effects of the vertical and/or horizontal seismic components of five different ground motions on the SMRFs were evaluated using incremental dynamic analysis. The proposed method accurately identified the severely damaged floors of SMRFs.
Youssef M.A., Chowdhury A.O., Meshaly M.E., 2015, “Seismic Capacity of Reinforced Concrete Interior Flat Plate Connections”, Bulletin of Earthquake Engineering, 13: 827-840.
Flat plates are widely used in reinforced concrete buildings. Their design is usually based on the shear forces and bending moments produced by the gravity loads. During seismic activities, the lateral building deformations induce additional shear forces and bending moments that they must withstand. To evaluate the seismic moment capacity of a flat plate system, an effective slab width needs to be defined. In this paper, grillage analysis is utilized to predict the nonlinear lateral behaviour of flat plate buildings. A comprehensive parametric study is used to evaluate the effective slab width contributing to the lateral strength of residential interior flat plate connections. The studied parameters include span length, bay width, column dimensions, and level of column axial load. Both gravity load designed frames and moment resisting frames are analysed. The effect of the material safety factors is assessed by conducting two sets of analyses using nominal material properties and factored material properties. Equations to estimate the effective slab width are proposed.
Sultana P., Youssef M.A., 2015, “Seismic Performance of Steel Moment Resisting Frames considering Horizontal and Vertical Seismic Components“, Proceedings of PROTECT2015 Conference on Response of Structures under Extreme Loading, Michigan State University, Paper ID 1343, pp. 463-470, 28-30 June 2015, Lansing, Michigan, USA.
Steel Moment Resisting Frames (SMRFs) are widely used to resist seismic loads. Different response parameters such as maximum roof drift, Maximum Interstorey Drift (MID), and plastic rotation of different frame elements are used to assess their seismic performance. This study investigates the variability of MID at collapse, evaluates the effect of vertical seismic component and identifies the critical floors. A ten storey SMRF was considered as a case study. Incremental dynamic analysis (IDA) was conducted using five different ground motions considering both the horizontal and vertical components. It was observed that the storey experiencing the MID is not always the severely damaged storey. The vertical seismic component was found to significantly increase the column axial forces and vertical deflection of the beams, and, thus increases the state of seismic damage in the frame. The effect of the vertical seismic component on the MID was also investigated.
Youssef M.A., Meshaly M.E., Chowdhury A.O., 2014, “Lateral Stiffness of Reinforced Concrete Interior Flat Plate Connections”, Engineering Structures, 62: 23-32.
Flat plates are widely used in reinforced concrete structures. To evaluate the lateral stiffness of a flat plate system, the contributing slab width needs to be defined. In this paper, a model that utilizes grillage analysis is proposed to predict the nonlinear lateral behaviour of flat plate structures. The model is then utilized to conduct a parametric study to evaluate the effective slab width contributing to the lateral stiffness of residential interior flat plate connections. The studied parameters are span length, bay width, column dimensions, and level of column axial load. Both gravity load designed frames and moment resisting frames are analysed. The effect of the material safety factors is assessed by conducting two sets of analyses using nominal material properties and factored material properties. Equations for estimating the effective slab width contributing to the lateral stiffness of the system are proposed.
Youssef M.A., Elfeki M.A., 2013, “Predicting Local Seismic Damage of RC Framed Buildings considering the Horizontal Seismic Component”, Magazine of Concrete Research, 65(23): 1411-1428.
This paper provides a simplified method to define local seismic damage for reinforced concrete frames considering the horizontal seismic component. The proposed method utilises static pushover analysis to evaluate the maximum and residual inter-storey drift limits for each storey. These limits are predicted for five frames and compared to experimental and analytical results by other researchers. Further validation of the method is achieved by conducting incremental dynamic analyses for a concrete frame using five earthquake records. Results have also provided an assessment of the use of residual and maximum inter-storey drifts to define collapse.
Elfeki M.A. and Youssef M.A., 2008, “Residual Capacity of Seismically Damaged Reinforced Concrete Moment Frames”, 2nd Canadian Conference on Effective Design of Structures CCEDS-II, Sustainability of Civil Engineering Structures, Hamilton, ON, Canada, pp. 613-621, DOI: 10.13140/2.1.3705.0886.
Reinforced Concrete (RC) structures are generally designed for safety conditions, where earthquake energy is dissipated through yielding of the reinforcement and its inelastic deformation. Their seismic behaviour has been the subject of extensive studies in the past two decades. The most common tool to assess their seismic damage is the Maximum Inter-storey Drift (MID). Due to the complexity involved in conducting nonlinear dynamic analysis, researchers recently emphasized that Residual Inter-storey Drift (RID) might be an easier alternative. This study aims at identifying differences arising from evaluating the seismic damage using MID and Maximum RID (MRID). A six-storey building designed and detailed according to current seismic codes is used in the study. Pushover analysis is conducted to define the collapse limit using both MID and MRID. The observed damage of the building at these limits when subjected to six earthquake records is obtained using nonlinear dynamic analysis. The two methods are found to be significantly different and it was concluded that the MRID is a better tool to judge on the seismic damage state of a building.
Youssef M.A. and Rahman M., 2007, “Simplified Seismic Modeling of RC Flexural Members“, Magazine of Concrete Research, 59(9): 639-649.
The need for simplified models that can accurately represent the behaviour of structures is increasing. Engineers need such models to assess and/or to design structures using pre-specified performance measures. In the current paper, the abilities of a previously developed model for reinforced concrete flexural members are significantly enhanced. The model represents a member by an elastic element and two inelastic end elements. Each inelastic element consists of three concrete and three steel springs. A rational approach to calculate the properties of these springs is developed. The approach includes a simplified method to account for slippage of reinforcing bars. The model allows identification of the localised damage (concrete cracking, reinforcement yielding, concrete crushing or bond slip failure) responsible for any change in the overall performance of a reinforced frame. To illustrate the use of this approach and to validate its predictions, two cantilever columns are modelled and analysed under monotonic and cyclic loadings.
El Naggar M.H., Youssef M.A., Ahmed M., 2007, “Monotonic and Cyclic Lateral Behaviour of Helical Pile Specialized Connectors”, Engineering Structures, 29(10): 2635-2640.
The helical pile is a foundation system used to support new residential and commercial buildings, and to stabilize repairs of existing structures. It also represents an attractive alternative to upgrade the seismic resistance of existing foundations. This paper is part of a comprehensive study to assess the seismic performance of foundations supported by helical piles. The paper presents an experimental study conducted to evaluate the seismic performance of the specialized connectors, linking the pile shaft to the concrete foundation, in the lateral direction. The paper also presents a simplified model that can be used to account for the connector behaviour while conducting seismic analysis of structures supported by helical piles.
Youssef M.A., EL Naggar M.H., Ahmed M., 2006, “Monotonic and Cyclic Load Behaviour of Helical Pile Connectors in the Vertical Direction“, Canadian Journal of Civil Engineering, 33(1): 10-18.
The helical pile is a foundation system that is used to support new residential and commercial buildings and to stabilize repairs of existing structures. It represents an attractive option to upgrade the seismic resistance of foundations. This necessitates a good understanding of the seismic performance of the specialized connectors linking the pile shaft to the concrete foundation. An experimental program is initiated at The University of Western Ontario to investigate the seismic performance of these connectors, to develop models that can be used in finite element analysis to describe their behaviour, and to propose modifications to enhance their seismic performance, if necessary. In this program, eight specimens were tested to assess the behaviour of two types of these connectors under different loading modes. It was concluded that connectors with an uplift bracket are required for seismic applications to control uplift displacement due to rocking of the foundation.Key words: helical pile, connector, experimental, model, monotonic load, cyclic load, foundation, stiffness, strength.
Youssef M.A., Ghaffarzadeh H., Nehdi M., 2007, “Seismic Performance of RC Frames with Concentric Internal Steel Bracing”, Engineering Structures, 29(7): 1561-1568.
Steel bracing has proven to be one of the most effective systems in resisting lateral loads. Although its use to upgrade the lateral load capacity of existing Reinforced Concrete (RC) frames has been the subject of numerous studies, guidelines for its use in newly constructed RC frames still need to be developed. In this paper, the efficiency of using braced RC frames is experimentally evaluated. Two cyclic loading tests were conducted on a moment frame and a braced frame. The moment frame was designed and detailed according to current seismic codes. A rational design methodology was adopted to design the braced frame including the connections between the brace members and the concrete frame. Test results showed that the braced frame resisted higher lateral loads than the moment frame and provided adequate ductility. The adopted methodology for designing the braced frame resulted in an acceptable seismic performance and thus represents the first step in the development of design guidelines for this type of frames.
Elfeki M.A. and Youssef M.A., 2007, “Effect of the Vertical Earthquake Component on the Seismic Response of Reinforced Concrete Moment Frames”, 9th Canadian Conference on Earthquake Engineering, June 26-29, Ontario, Canada, paper 1129, 10 pp, DOI: 10.13140/2.1.2656.5120.
The seismic behaviour of multi-storey Reinforced Concrete (RC) structures under the effect of horizontal excitations has been the subject of extensive studies over the last several decades. Due to the increase in near-source records, researchers recently emphasized the importance of the vertical earthquake component. In this paper, a comparative study of the inelastic seismic performance of a six-storey RC building under the effect of the horizontal earthquake component and both the horizontal and vertical components is carried out. Six earthquake records are used to study the global and local inelastic behaviour of the building. It is concluded that considering the vertical component does not have significant effect on the computed drift, but greatly affects the distribution and intensity of local damage. It is essential to include the vertical component of earthquakes to accurately predict the ductility of the structure and its expected failure mechanism.
Nehdi M., Youssef M.A., Ghaffarzadeh H., 2005, “Experimental Evaluation of the Seismic Behavior of Steel-braced RC Frames”, Proceedings of the 7th International Conference on Multipurpose High-Rise Towers and Tall Buildings (IFHS), Dec. 10-11, Dubai, UAE, Paper IFHS-211, 7 pp.
Steel bracing has proven to be one of the most effective systems in resisting lateral loads. Although its use to upgrade the lateral load capacity of existing Reinforced Concrete (RC) frames has been the subject of numerous studies, guidelines for its use in newly constructed RC frames still need to be developed. In this paper, the efficiency of using braced RC frames is experimentally evaluated. A cyclic loading test was conducted on a braced frame. A rational design methodology was adopted to design the frame including connections between the brace members and the concrete frame. Test results showed that the braced frame provided adequate energy dissipation. The adopted methodology for designing the braced frame resulted in an acceptable seismic performance and thus represents the first step in the development of design guidelines for this type of frames.
Youssef M. and Ghobarah A., 2001, “Modelling of RC Beam-Column Joints and Structural Walls“, Journal of Earthquake Engineering, 5(1): 93-111.
The deformation of beam-column joints may contribute significantly to drift of reinforced concrete (RC) frames. In addition, failure may occur in the joints due to cumulative concrete crushing from applied beam and column moments, bond slip of embedded bars or shear failure as in the case of existing frames with nonductile detailing. When subjected to earthquake loading, failure in RC structural wall is similar to failure of frame joints as it may occur due to cumulative crushing from high flexural stresses, bond slip failure of lap splice, shear failure or a combination of various mechanisms of failure. It is important to include these behavioural characteristics in a simple model that can be used in the analysis of RC frames and RC walls to predict their response under earthquake loading and determine their failure modes. Global macro models for the beam-column joint and for RC structural walls are developed. The proposed models represent shear and bond slip deformations as well as flexural deformations in the plastic hinge regions. The models are capable of idealising the potential failure mechanism due to crushing of concrete, bond slip or shear with allowance for the simultaneous progress in each mode. The model predictions are compared with available experimental data and good correlation is observed between analytical results and the test measurements.
Ghobarah A. and Youssef M., 2000, “Rehabilitation of RC Buildings using Structural Walls “, 12th World Conference on Earthquake Engineering, Auckland, New Zealand, paper No. 153, 8 pp, DOI: 10.13140/2.1.2534.6566.
A developed macroscopic model is applied to the analysis of an example structure to demonstrate the use and advantages of the model. The lateral capacity of a three storeys reinforced concrete (RC) building before and after rehabilitation was assessed using pushover analysis and nonlinear dynamic analysis. The nonlinear dynamic time history analysis was conducted using El Centro record during the Imperial Valley earthquake scaled to different peak ground accelerations (PGA). A rehabilitation technique using structural walls was designed and tested using pushover analysis and nonlinear dynamic analysis with the El Centro record as the ground motion time history input.
Youssef M. and Ghobarah A., 1999, “Strength Deterioration due to Bond Slip and Concrete Crushing in Modeling of Reinforced Concrete Members“, ACI Structural Journal, 96(6): 956-966.
In the design process of a new structure or in the seismic assessment of an existing structure, the model plays an important role. There are several available models that represent the flexural behavior of columns to various degrees of accuracy. An efficient model is needed, however, for the simple and accurate representation of the behavior up to failure. A macromodel that represents the behavior of reinforced concrete members that accounts for strength degradation due to bond slip and crushing of concrete is developed. The model consists of nonlinear springs connected by rigid elements. The defined models for these springs are capable of describing the hysteretic characteristics of reinforced concrete structures with sufficient accuracy. Moreover, the element model is capable of idealizing the potential failure mechanism due to crushing of concrete or bond slip or both occurring simultaneously. The model response predictions are verified to be in close agreement with experimental measurements.
Ghobarah A. and Youssef M., 1999, “Modelling of Reinforced Concrete Structural Walls“, Engineering Structures, 21(10): 912-923.
The reinforced concrete structural wall is an important lateral load resisting element. It is increasingly used by designers in new structures as well the rehabilitation of existing ones. There are models that represent the flexural behaviour of walls to various degrees of accuracy. However, an efficient model is needed for accurate representation of the flexural and shear behaviour of these walls. A macro model that represents the behaviour of structural walls is developed. The model consists of nonlinear springs connected by linear beam elements. The defined models of these springs are capable of describing the hysteretic characteristics of reinforced concrete structures with sufficient accuracy. Moreover, the model is capable of idealizing both shear and flexural behaviours of reinforced concrete structural walls. The model response predictions are verified to be in close agreement with experimental measurements.
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