( 1 ) NONLINEAR ANALYSIS OF OFFSHORE STRUCTURES UNDER WAVE LOADINGS

Transcription

1 ( 1 ) NONLINEAR ANALYSIS OF OFFSHORE STRUCTURES UNDER WAVE LOADINGS Shehata E. Abdel Raheem, Elsayed M. A. Abdel Aa, Aly G. A. Abdel Shafy and Fayez K. Abdel Seed The structural design requirements of an offshore platform subjected wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under wave loading is presented, the structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform. Offshore Structures, Sea waves, Nonlinear Analysis, Finite Element Analysis, Wave-Structure Interaction. Journal of Engineering Sciences, Vol..40 -No..3, page 1 / 13

2 ( 2 ) SHEAR RESPONSE INVESTIGATION OF HSRC DEEP BEAMS WITHOUT WEB REINFORCEMENT PART I: COMPARISON OF DESIGN EQUATIONS Aly G. Aly Abd-Elshafy, Ahmed I. Ramadan, Mahmoud H. Ahmed and Atif M. Abdel-Hafez Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems are usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches like ACI, Canadian, FIB and the method proposed by Sudheer, Zararis,Zsutty,Shah,Bazant and Russo. Eighteen simple span high strength reinforced concrete HSRC deep beams without web reinforcement were tested and analyzed under two static point loads at mid-span of the beam to examine the contribution of various parameters on the shear capacity of HSRC beams. The main studied parameters are f cu=50 MPa, three values of tension reinforcement-ρ%-(0.73%,1.21% &1.83%) and shear span to effective depth ratio-a/d-( 2,1.5 &1). As a conclusion of this paper, ACI and FIB code provisions for shear in HSC are safe for use with the exception that CSA should be used with care. Despite numerous studies, there is still a need to develop a clear understanding of the shear behavior of HSC beams without web reinforcement. Therefore, this experimental program was arranged to evaluate the shear behavior and to increase the shear database on HSRC deep beams. deep beams, high strength concrete, tension reinforcement ratio, shear span to effective depth ratio, shear strength. Journal of Engineering Sciences, Assiut University, Faculty of Engineering, 41-4, page 2 / 13

3 ( 3 ) Shear response investigation of HSRC deep beams without web reinforcement. Part I: design equations Ahmed Ramadan, Aly G. Aly Abd-Elshafy, Mahmoud H. Ahmed; Atif M. Abdel-Hafez Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems rely on design is usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches like ACI (FIP,1996), Canadian (CSA,1994),FIB (1999),and the method proposed by Sudheer (2011), Zararis (2003),Zsutty (1971),Shah (2009),Bazant (1984),and Russo (2005) have been calculated and analyzed on 18 simple span HSRC deep beams without web reinforcement were tested under monotonic two point loads at the mid span to examine the contribution of various parameters on the shear capacity of HSRC beams like; f cu=50 MPa, three values of tension reinforcement (0.73%,1.21% &1.83%) and shear span to effective depth ratio-a/d-( 2,1.5 &1) were selected to mainly study the behavior of deep beams, where typical shear failure can be anticipated. ACI and FIB code provisions for shear in HSC are safe for use with the exception that CSA should be used with care; it might have a tight safety margin against brittle shear failures. deep beam, high strength concrete, shear strength, tension reinforcement ratio, shear span to effective depth ratio, code design equations International Journal of Advanced Engineering Applications, 5-5, page 3 / 13

4 ( 4 ) Shear response investigation of HSRC deep beams without web reinforcement. Part II Beam characteristics Ahmed I. Ramadan, Aly G. Aly Abd-Elshafy,and Atif M. Abdel-Hafez ACI code specifies the shear strength of deep beams based on the strength at the first diagonal crack of NSC beams without the consideration of beam size effect. Therefore, it is necessary to evaluate if the ACI design equation for deep beams is applicable to high strength reinforced concrete (HSRC) deep beams with main reinforcement ratio less and more than 1% with considering size effect or not. This paper is considered a supplement to the companion paper (Part I Comparison of Design Equations). Eighteen simple span HSRC deep beams without stirrups were tested to examine various parameters on the shear capacity; f cu=50 MPa, three values of main reinforcement, (ρs%), (0.73%,1.21% &1.83%) and four values of shear span to overall depth ratio, (a/h), ( 0.84,1.3,1.7&2.3) were selected to mainly study the characteristics of deep beams. The increase in overall depth (h) under the same a/h=1.3&1.7, led to more brittle failure with wide diagonal cracks and high energy release rate related to size effects. HSRC deep beams exhibited more remarkable size effects with regard to brittle behavior. It was also shown that the ACI code gives similar safety factors on the shear strength at the first diagonal crack of HSRC deep beams, but do not specify a high enough safety factor on their ultimate strength due to the size effects. deep beam, high strength concrete, first diagonal crack, ultimate strength, Beam characteristics International Journal of Advanced Engineering Applications, 4-6, page 4 / 13

5 ( 5 ) Do ACI & JSCE codes emphasize the characteristics of high strength reinforced concrete deep beams or need reevaluation? Ahmed I. Ramadan and Aly G. Abd-Elshafy This paper summarize and analyzie the shear charactaristics of tested beams according to provisions of ACI & JSC codes which both of them specifie the shear strength of deep beams based on the first diagonal crack strength of normal strength concrete NSC beams without taken into account the beam size effect. Hence, it is substantial to evaluate the applicability of JSCE & ACI shear design equations to high strength reinforced concrete (HSRC) deep beams with main steel ratio less and more than 1% with considering beam size effect or not. f c=60 MPa, three values of main reinforcement, (ρs%), (0.73,1.21 &1.83) and shear span to overall depth ratio, (a/h), ( 0.84,0.87,1.3 &1.7) were selected to study the shear characteristics of 18 simple span deep beams without stirrups. The increase in overall depth (h) under the same a/h=1.3&1.7, led to more brittle failure with wide diagonal cracks. HSRC deep beams exhibited more remarkable size effects with regard to brittle behavior. It was also shown that the ACI code gives similar safety factors on the shear strength at the first diagonal crack of HSRC deep beams, but do not specify a high enough safety factor on their ultimate strength due to the size effects. deep beams, HSC, main steel ratio, shear span to effective depth ratio and shear strength International Conference on Advances in Structural and Geotechnical Engineering, 6-9 April 2015, Hurghada, EgypT, NULL, NULL page 5 / 13

6 ( 6 ) Evaluation of Shear Strength of HSRC beams without web reinforcement Ahmed Ramadan, Aly G. Aly Abd-Elshafy, Mahmoud H. Ahmed, Atif M. Abdel-Hafez Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems rely on design is usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches [1-10] have been calculated and analyzed on 18 simple span HSRC deep beams without web reinforcement were tested under monotonic two point loads at the mid span to examine the contribution of various parameters on the shear capacity of HSRC beams like; f cu=50 MPa, three values of tension reinforcement (0.73%,1.21% &1.83%) and shear span to effective depth ratio ( 2,1.5 &1) were selected to mainly study the behavior of deep beams, where typical shear failure can be anticipated. NULL CSM 2013-Second International Conference on Advances in Civil, Structural and Mechanical Engineering, Hotel L-Nina et Convention Center - HongKong; 08/2013, NULL, NULL page 6 / 13

7 ( 7 ) Evaluation of Shear Strength of HSRC beams without web reinforcement Ahmed Ibrahim Hassan Ramadan Aly Gamal Ali Abd-Elshafy Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems rely on design is usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches have been calculated and analyzed on 18 simple span HSRC deep beams without web reinforcement were tested under monotonic two point loads at the mid span to examine the contribution of various parameters on the shear capacity of HSRC beams like; fcu=60 MPa, three values of tension reinforcement (0.73%,1.21% &1.83%) and shear span to effective depth ratio ( 2,1.5 &1) were selected to mainly study the behavior of deep beams, where typical shear failure can be anticipated. deep beams, HSC, tension reinforcement ratio, shear span to effective depth ratio and shear strength The ninth Alexandria international conference on Structural and Geotechnical Engineering, Vol.1, 1-12 page 7 / 13

8 ( 8 ) Seismic performance of L-shaped multi-storey buildings with moment-resisting frames Shehata E. Abdel Raheem, Momen M. M. Ahmed, Mohamed M. Ahmed and Aly G. A. Abdel Shafy Recent earthquakes have demonstrated that buildings with irregular configuration are more vulnerable to earthquake damage. Moreover, the configuration irregularities introduce major challenges in the seismic design of building structures. One such form of irregularity is the presence of re-entrant corners and torsional irregularity that causes stress concentration due to sudden changes in stiffness and torsion amplification in buildings. Constructive research into re-entrant corner and torsionirregular buildings is therefore needed to evaluate the seismic response demands for reducing the potential damage. The aim of the study reported in this paper is to grasp the seismic performance of L-shaped irregular buildings with moment-resisting frames through an evaluation of the irregularity effects on measured seismic response demands. The results for inter-storey drift, storey shear force, overturning moment, torsion moment responses at the base and along the building height, top-floor displacement and torsional irregularity coefficient prove that buildings with irregularity are more vulnerable than those with a regular configuration resulting from stress concentration and coupled lateral torsional behaviour. buildings, structures & design mathematical modelling seismic engineering Proceedings of the Institution of Civil Engineers - Structures and Buildings, Vol No. 5, pp page 8 / 13

9 ( 9 ) Evaluation of plan configuration irregularity effects on seismic response demands of L-shaped MRF buildings Shehata E. Abdel Raheem, Momen M. M. Ahmed Mohamed M. Ahmed, Aly G. A. Abdel-shafy 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 reentrant 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. Plan configuration irregularity L-shaped buildings Seismic design demands Torsional irregularity ratio Bulletin of Earthquake Engineering, Vol No. 9, pp page 9 / 13

10 ( 10 ) Irregularity Effects on the Seismic Performance of L-Shaped Multi-Story Buildings Momen M. M. Ahmed, Shehata E. Abdel Raheem, Mohamed M. Ahmed and Aly G. A. Abdel Shafy Past and recent earthquakes events demonstrate that buildings with configuration irregularity are more vulnerable to earthquake damages. So it's essential to investigate the seismic response of these structures in active seismic zones to reduce the potential seismic damages. The configuration irregularities introduce major challenges in the seismic design of building structures. One such form of irregularity is the presence of re-entrant corners that causes stress concentration due to sudden changes in stiffness and torsion amplification in the buildings; hence causes early collapse. This, the conventional design codes have not recommendations for proper evaluation of these buildings yet. Thus, a constructive research into re-entrant corner irregularity problems is essentially needed greater than ever. The objective of this study is to grasp the seismic behavior of the buildings with irregular plan of L-shape floor plan through the evaluation of the configuration irregularity of reentrant corners effects on measured seismic response demands. The measured responses include inter-story drift; story shear force; overturning moment; torsion moment at the base and along the building height; top floor displacement; and torsional Irregularity Ratio. Three dimensional finite element model of nine stories moment resisting frame buildings as reference model is developed; six L-shaped models are formulated with gradual reduction in the plan of the reference model. The models are analyzed with ETABS using Equivalent Static Load (ESL) and Response Spectrum (RS) Methods. The results prove that buildings with severe irregularity are more vulnerable than those with regular configuration resulting from torsion behavior, and the additional shear force produced in the perpendicular direction to the earthquake input. Also, in the codal empirical equation for the calculation of fundamental period of vibration could not grasp significant higher vibration modes such as torsional vibration of irregular buildings that could significantly affect seismic demands. Configuration Irregularity; L-shaped Buildings; Seismic demands; Torsional Irregularity Ratio Journal of Engineering Sciences, Assiut University, 44-5, page 10 / 13

11 ( 11 ) NUMERICAL ANALYSIS OF SEISMIC POUNDING BETWEEN ADJACENT BUILDINGS Mohammed Y.M. Fooly, Shehata E. Abdel Raheem, Aly G.A. abdelshafy, Yousef A. Abbas and Mohamed S. AbdelLatif Seismic vulnerability assessments of buildings after several earthquakes have confirmed that the pounding could be one of the key threats. The pounding among series of neighbouring building structures throughout earthquakes exerts repeated strikes on each other that could be a reason for structural damages ranging from light damage to even collapse. So, the main objectives are to provide constructive suggestions for code calibration through a numerical simulation for the estimation of the pounding risks on series of neighbouring buildings separated by minimum code-specified separation. A numerical simulation and FE analysis are developed to estimate the influence of pounding on the seismic response demands of adjacent buildings. The collision effects on 3-, 6- and 12-stories adjacent buildings are studied for different separation distances and alignment configurations and compared with a nominal model without pounding considerations. Based on the obtained results, it is concluded that the seriousness of the impact effects is influenced by the vibration characteristics of the adjacent buildings, the input excitation characteristics and whether the building is exposed to one- or two-sided impacts. There are additional loads caused by the pounding which leads to additional shear forces and acceleration at different story levels that do not appear in the no-pounding case. Adjacent buildings in series; Seismic pounding; Time history analysis; Separation gap; response demands. International Conference on Mathematics and its Applications (ICMA18), NULL, NULL page 11 / 13

12 ( 12 ) Seismic pounding effects on adjacent buildings in series with different alignment configurations Shehata E. Abdel Raheem, Mohamed Y.M. Fooly, Aly G.A. Abdel Shafy, Yousef A. Abbas, Mohamed Omar, Mohamed M.S. Abdel Latif,Sayed Mahmoud Numerous urban seismic vulnerability studies have recognized pounding as one of the main risks due to the restricted separation distance between neighboring structures. The pounding effects on the adjacent buildings could extend from slight non-structural to serious structural damage that could even head to a total collapse of buildings. Therefore, an assessment of the seismic pounding hazard to the adjacent buildings is superficial in future building code calibrations. Thus, this study targets are to draw useful recommendations and set up guidelines for potential pounding damage evaluation for code calibration through a numerical simulation approach for the evaluation of the pounding risks on adjacent buildings. A numerical simulation is formulated to estimate the seismic pounding effects on the seismic response demands of adjacent buildings for different design parameters that include: number of stories, separation distances; alignment configurations, and then compared with nominal model without pounding. Based on the obtained results, it has been concluded that the severity of the pounding effects depends on the dynamic characteristics of the adjacent buildings and the input excitation characteristics, and whether the building is exposed to one or two-sided impacts. Seismic pounding among adjacent buildings produces greater acceleration and shear force response demands at different story levels compared to the no pounding case response demands. Adjacent buildings in series; seismic pounding; time history analysis; separation gap; response demands; alignment configurations Steel and Composite Structures, Vol No. 3, pp page 12 / 13

13 Powered by TCPDF ( Assiut university ( 13 ) Numerical simulation of potential seismic pounding among adjacent buildings in series Shehata E Abdel Raheem, Mohammed YM Fooly, Aly GA Abdel Shafy, Ahmed M Taha, Yousef A Abbas, Mohamed MS Abdel Latif Numerous urban seismic vulnerability studies have recognized pounding between adjacent structures as one of the main risks for neighbouring buildings due to the restricted separation distance. The seismic pounding could produce damages that range from slight non-structural to serious structural damage that could even head to a total collapse of buildings. Therefore, an assessment of the seismic pounding risk of buildings is indispensable in future calibration of seismic design code provisions. Thus, this study targets to draw useful recommendations for seismic design through the evaluation of the pounding effects on adjacent buildings. A numerical simulation is formulated to estimate the pounding effects on the seismic response demands of three adjacent buildings in series with different alignment configurations. Three adjacent buildings of 3-storey, 6-storey and 12-storey MRF buildings are combined together to produce three different alignment configurations; these configurations of adjacent buildings are subjected to nine ground motions that are absolutely compatible with the design spectrum. The nonlinear time-history is performed for the evaluation of the response demands of different alignment configurations of the adjacent buildings using structural analysis software ETABS. Various response parameters are investigated such as displacement, acceleration, storey shear force mean and maximum responses, impact force and hysteretic behaviour. Based on the obtained results, it has been concluded that the severity of the seismic pounding effects depends on the vibration characteristic of the adjacent buildings, the input excitation characteristic and whether the building has interior or exterior alignment position, thus either exposed to one or two-sided impacts. Seismic pounding among adjacent buildings induces greater shear force and acceleration response demands at different story levels for the high rise building, while the response could be reduced in the short buildings compared to that of no-pounding case. The effect of poundings of adjacent buildings seems to be critical for most of the cases and, therefore, the structural pounding phenomenon is rather detrimental than beneficial. Adjacent buildings in series Seismic pounding Time history analysis Separation gap Response demands Earthquake characteristics Bulletin of Earthquake Engineering, Vol No. 12, pp page 13 / 13