Soil conditions have a great deal to do with damage to structures during earthquakes. Hence the investigation on the energy transfer mechanism from soils to buildings during earthquakes is critical for the seismic design of multi-story buildings and for upgrading existing structures. Thus, the need for research into soil–structure interaction (SSI) problems is greater than ever. Moreover, recent studies show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of foundation neglecting the flexibility of the foundation, the compressibility of the underneath soil and, consequently, the effect of foundation settlement on further redistribution of bending moment and shear force demands. Hence the SSI analysis of multi-story buildings is the main focus of this research; the effects of SSI are analyzed for typical multi-story building resting on raft foundation. Three methods of analysis are used for seismic demands evaluation of the target moment-resistant frame buildings: equivalent static load; response spectrum methods and nonlinear time history analysis with suit of nine time history records. Three-dimensional FE model is constructed to investigate the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of building structures. Numerical results obtained using SSI model with different soil conditions are compared to those corresponding to fixed-base support modeling assumption. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed. The results of different analysis approaches are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis.

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Evaluation of soil–foundation–structure interaction effects on seismic response demands of multi-story MRF buildings on raft foundations

Damage assessments after past earthquakes have frequently revealed that plan configuration irregular buildings have more severe damage due to excessive torsional responses and stress concentration than regular buildings. The plan configuration irregularities introduce major challenges in the seismic design of buildings. One such form of irregularity is the presence of re-entrant corners in the L-shaped buildings that causes stress concentration due to sudden changes in stiffness and torsional response amplification; hence causes early collapse. A constructive research into re-entrant corner and torsional irregularity problems is essentially needed greater than ever. Therefore, the focus of this study is to investigate structural seismic response demands for the class of L-shaped buildings through evaluating the plan configuration irregularity of re-entrant corners and lateral–torsion coupling effects on measured seismic response demands. The measured responses include story drift, inter-story drift, story shear force, overturning moment, torsion moment at the base and over building height, and torsional irregularity ratio. Three dimensional finite element model for nine stories symmetric buildings as reference model is developed. In addition, six L-shaped building models are formulated with gradual reduction in the plan of the reference building model. The results prove that building models with high irregularity are more vulnerable due to the stress concentration and lateral torsional coupling behavior than that with regular buildings. In addition, the related lateral shear forces in vertical resisting elements located on the periphery of the L-shaped buildings could be significantly increased in comparison with the corresponding values for a symmetric building.

Evaluation of plan configuration irregularity effects on seismic response demands of L-shaped MRF buildings

A new model based on Artificial Neural Network (ANN) was established as a trustworthy technique for predicting ultimate lateral torsional buckling (LTB) capacity of castellated steel beams. The required information for training, validating and testing of the developed model obtained from a reliable database. Consequently, a new formulation based on the ANN has been offered for predicting the failure load of castellated steel beams exposed to LTB. All parameters which may affect the LTB capacity of castellated beams were considered for presentation of this formula. Then, outcomes of the proposed formula were compared with predictions of Australian Standard (AS4100) for LTB capacity of castellated beams. This comparison indicated that proposed formula has a good performance for prediction of ultimate strength in castellated beams subjected to LTB. At the end, Garson’s algorithm has been established as a sensitivity analysis to determinate importance of each input in the proposed formula.

Lateral Torsional Buckling Capacity Assessment of Castellated Steel Beams Using Artificial Neural Networks

The response spectrum method (RSM) has been incorporated into many codes for seismic design of aboveground structures since 1950s. However, no RSM is presented in details for the seismic design of underground structures due to the complexity of seismic soil–structure interaction (SSI). In this paper, the RSM is developed for the seismic analysis of the underground structures including SSI. First, the underground design response spectrum is derived using two different procedures from the ground design response spectrum that is commonly available in most seismic design codes. Second, the SSI analysis model consisting of the underground structure and its adjacent soil is established with the roller side boundaries and the bottom boundary subjected to the underground response spectrum. Third, the RSM is applied to the SSI analysis model to estimate the structural response under the underground response spectrum. Finally, the numerical examples are presented to demonstrate the feasibility of the RSM for the SSI analysis model of underground structure.

Response spectrum method for seismic soil–structure interaction analysis of underground structure

Half-through girders are not affected by conventional lateral-torsional buckling. I-section beams of simply supported half-through girders experience compression in their top flanges and tension in their bottom flanges. In this condition, the compression flange is restrained only by the stiffness of the web, and the buckling mode is generally restrained distortional. In this study, new and efficient model is derived to predict the Restrained Distortional Buckling (RDB) strength of half-through I-section bridge girders utilizing an Artificial Neural Network (ANN). The model is developed based on a reliable database obtained from the nonlinear finite element (FE) method. To verify the accuracy of the derived model, it is applied to estimate the RDB strength of parts of the FE analysis results that were not included in the modeling process. A sensitivity analysis has been also developed to determine the importance of each input parameters. ANN model is further compared to the some existing design codes. The results indicate that the proposed model is effectively capable of evaluating the RDB load of the half-through girders. The prediction performance of the ANN model is markedly better than prediction of the AISC/LRFD and the AS4100 specifications. The ANN-based design equation can reliably be employed for pre-design applications.

A new predictive model for restrained distortional buckling strength of half-through bridge girders using artificial neural network

The investigation on the energy transfer mechanism from soils to buildings during earthquakes is critical for the design of earthquake resistant structures and for upgrading existing structures. Thus the need for research into Soil-Structure Interaction (SSI) problems is greater than ever. Moreover, recent studies show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of foundation neglecting the flexibility of the foundation, the compressibility of soil mass and consequently the effect of foundation settlement on further redistribution of bending moment and shear force demands. Hence the soil-structure interaction analysis of multi-story buildings is the main focus of this study; the effects of SSI are analyzed for typical multi-story building resting on raft foundation. Three methods of analysis are used for seismic demands evaluation of the target moment resistant frame buildings: equivalent static load (ESL); response spectrum (RS) methods and nonlinear time history (TH) analysis with suit of nine time history records. Three-dimensional FEM model is constructed to analyze the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of building structures. Numerical results obtained using soil structure interaction model conditions are compared to those corresponding to fixed-base support conditions. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed. The analysis results of different approaches are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis.

https://jesaun.journals.ekb.eg/article_111441_cb81cb9296ecb0cd0df91d94e9c85f90.pdf

Soil-Structure Interaction Effects on Seismic Response of multi-story Buildings on Raft Foundation

Recent studies show that the effects of Soil Structure Interaction (SSI) may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of foundation ne- glecting the flexibility of the foundation, the compressibility of soil mass and consequently the effect of foun- dation settlement on further redistribution of bending moment and shear force demands. The effects of SSI are analyzed for typical multi-story building resting on raft foundation. Three methods of analysis are used for seismic demands evaluation of the target moment resistant frame buildings: equivalent static load (ESL); response spectrum (RS) methods and nonlinear time history (TH) analysis with suit of nine time history records. Three-dimensional Finite Element (FE) model is constructed to analyze the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of build- ing structures. Numerical results obtained using soil structure interaction model conditions are compared to those corresponding to fixed-base support conditions. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed.

Soil-raft foundation-structure interaction effects on seismic performance of multi-story mrf buildings

In urban cities, buildings were built in the neighborhood, these buildings influence each other through structure-soil-structure interaction (SSSI) and seismic pounding due to limited separation distance in-between. Generally, the effects of the interaction between soil and structure are disregarded during seismic design and analysis of superstructure. However, the system of soil-base adversely changes structural behavior and response demands. Thus, the vibration characteristics plus the seismic response of a building are not able to be independent of those in adjacent buildings. The interaction between structure, soil, and structure investigates the action of the attendance of adjacent buildings to the others by the interaction effect of the sub-soil under dynamic disturbances. The main purpose of this research is to analyze the effects of SSSI and seismic pounding on the behavior of adjacent buildings. The response of a single structure or two adjacent structures with shallow raft base lying on soft soil are studied. Three dimensions finite element models are developed to investigate the effects of pounding; gap distance; conditions of soil; stories number; a mass of adjacent building and ground excitation frequency on the seismic responses and vibration characteristics of the structures. The variation in the story displacement, story shear, and story moment responses demands are studied to evaluate the presence effect of the adjacent buildings. Numerical results acquired using conditions of soil models are compared with the condition of fixed support and adjacent building models to a single building model. The peak responses of story displacement, story moment, and story shear are studied.

Tarek M. A. Alazrak

Papers

Evaluation of soil–foundation–structure interaction effects on seismic response demands of multi-story MRF buildings on raft foundations

Soil-Structure Interaction Effects on Seismic Response of multi-story Buildings on Raft Foundation

Soil-raft foundation-structure interaction effects on seismic performance of multi-story mrf buildings

Seismic pounding between adjacent buildingsconsidering soil-structure interaction