Response spectrum analysis for regular base isolated buildings subjected to near fault ground motions

Moussa, Leblouba Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.4

This paper presents a response spectrum analysis procedure suitable for base isolated regular buildings subjected to near fault ground motions. This procedure is based on the fact that the isolation system may be treated separately since the superstructure behaves as a rigid body on well selected isolation systems. The base isolated building is decomposed into several single-degree of freedom systems, the first one having the total weight of the building is isolated while the remainder when superposed they replicate approximately the behavior of the superstructure. The response of the isolation system is governed by a response spectrum generated for a single isolated mass. The concept of the procedure and its application for the analysis of base isolated structures is illustrated with an example. The present analysis procedure is shown to be accurate enough for the preliminary design and overcomes the limits of applicability of the conventional linear response spectrum analysis.

Response spectrum analysis for regular base isolated buildings subjected to near fault ground motions

Leblouba Moussa 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.4

This paper presents a response spectrum analysis procedure suitable for base isolated regular buildings subjected to near fault ground motions. This procedure is based on the fact that the isolation system may be treated separately since the superstructure behaves as a rigid body on well selected isolation systems. The base isolated building is decomposed into several single-degree of freedom systems, the first one having the total weight of the building is isolated while the remainder when superposed they replicate approximately the behavior of the superstructure. The response of the isolation system is governed by a response spectrum generated for a single isolated mass. The concept of the procedure and its application for the analysis of base isolated structures is illustrated with an example. The present analysis procedure is shown to be accurate enough for the preliminary design and overcomes the limits of applicability of the conventional linear response spectrum analysis.

Ductility and inelastic deformation demands of structures

Benazouz, Cheikh,Moussa, Leblouba,Ali, Zerzour Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.5

Current seismic codes require from the seismically designed structures to be capable to withstand inelastic deformation. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformation and performance of structures. Recently, the concept of inelastic spectra has been adopted in the global scheme of the performance-based seismic design through capacity-spectrum methods. In this paper, the median of the ductility demand ratio for 80 ground motions are presented for different levels of normalized yield strength, defined as the yield strength coefficient divided by the peak ground acceleration (PGA). The influence of the post-to-preyield stiffness ratio on the ductility demand is investigated. For fixed levels of normalized yield strength, the median ductility versus period plots demonstrated that they are independent of the earthquake magnitude and epicentral distance. Determined by regression analysis of the data, two design equations have been developed; one for the ductility demand as function of period, post-to-preyield stiffness ratio, and normalized yield strength, and the other for the inelastic deformation as function of period and peak ground acceleration valid for periods longer than 0.6 seconds. The equations are useful in estimating the ductility and inelastic deformation demands for structures in the preliminary design. It was found that the post-to-preyield stiffness has a negligible effect on the ductility factor if the yield strength coefficient is greater than the PGA of the design ground motion normalized by gravity.

Experimental and analytical study on the shear strength of corrugated web steel beams

Samer Barakat,Moussa Leblouba 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.2

Compared to conventional flat web I-beams, the prediction of shear buckling stress of corrugated web steel beams (CWSBs) is not straightforward. But the CWSBs combined advantages of lightweight large spans with low-depth high load-bearing capacities justify dealing with such difficulties. This work investigates experimentally and analytically the shear strength of trapezoidal CWSBs. A set of large scale CWSBs are manufactured and tested to failure in shear. The results are compared with widely accepted CWSBs shear strength prediction models. Confirmed by the experimental results, the linear buckling analyses of trapezoidal corrugated webs demonstrated that the local shear buckling occurs only in the flat plane folds of the web, while the global shear buckling occurs over multiple folds of the web. New analytical prediction model accounting for the interaction between the local and global shear buckling of CWSBs is proposed. Experimental results from the current work and previous studies are compared with the proposed analytical prediction model. The predictions of the proposed model are significantly better than all other studied models. In light of the dispersion of test data, accuracy, consistency, and economical aspects of the prediction models, the authors recommend their proposed model for the design of CWSBs over the rest of the models.

Ductility and inelastic deformation demands of structures

Cheikh Benazouz,Leblouba Moussa,Zerzour Ali 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.5

Current seismic codes require from the seismically designed structures to be capable to withstand inelastic deformation. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformation and performance of structures. Recently,the concept of inelastic spectra has been adopted in the global scheme of the performance-based seismic design through capacity-spectrum methods. In this paper, the median of the ductility demand ratio for 80 ground motions are presented for different levels of normalized yield strength, defined as the yield strength coefficient divided by the peak ground acceleration (PGA). The influence of the post-to-preyield stiffness ratio on the ductility demand is investigated. For fixed levels of normalized yield strength, the median ductility versus period plots demonstrated that they are independent of the earthquake magnitude and epicentral distance. Determined by regression analysis of the data, two design equations have been developed; one for the ductility demand as function of period, post-to-preyield stiffness ratio, and normalized yield strength, and the other for the inelastic deformation as function of period and peak ground acceleration valid for periods longer than 0.6 seconds. The equations are useful in estimating the ductility and inelastic deformation demands for structures in the preliminary design. It was found that the post-to-preyield stiffness has a negligible effect on the ductility factor if the yield strength coefficient is greater than the PGA of the design ground motion normalized by gravity.

Experimental investigation on the hysteresis behavior of the wire rope isolators

P. S. Balaji,Leblouba Moussa,M. E. Rahman,Loo Tshun Vuia 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.4

Vibration isolation has been widely applied to filter the external excitation energy and impact forces in building structures and equipment. Wire rope isolator (WRI), a kind of isolator for vibration and shock isolation, shows a better performance in attenuating theseforces. WRIs are able to deviate these external forces through their mechanical configuration and high-energy dissipative capabilities. The application of WRI demands knowledge of its behavior and the relation between various geometrical properties and input force. Thepresent work investigates the influence of geometrical parameters, such as wire rope diameter, number of coils, and displacement amplitudeon the hysteresis behavior of WRI under quasi-static loading in both vertical and horizontal directions. The hysteresis behavior ofdifferent WRIs was evaluated using the calculated parameters from hysteresis force-displacement curves: energy loss ratio (ELR), andeffective stiffness. The study indicates that the geometric properties significantly influence the effective stiffness than the energy lossratio. It is observed that, increased displacement amplitude results in decreased ELR and hence damping capabilities. The study alsoconfirms that the wire rope isolator possesses a good ability in damping through its stiffness and high-energy dissipation capability.

An analytical study on the static vertical stiffness of wire rope isolators

P. S. Balaji,Leblouba Moussa,M. E. Rahman,Lau Hieng Ho 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.1

The vibrations caused by earthquake ground motions or the operations of heavy machineries can affect the functionality of equipmentand cause damages to the hosting structures and surrounding equipment. A Wire rope isolator (WRI), which is a type of passive isolatorknown to be effective in isolating shocks and vibrations, can be used for vibration isolation of lightweight structures and equipment. Theprimary advantage of the WRI is that it can provide isolation in all three planes and in any orientation. The load-supporting capability ofthe WRI is identified from the static stiffness in the loading direction. Static stiffness mainly depends on the geometrical and materialproperties of the WRI. This study develops an analytical model for the static stiffness in the vertical direction by using Castigliano’s secondtheorem. The model is validated by using the experimental results obtained from a series of monotonic loading tests. The flexuralrigidity of the wire ropes required in the model is obtained from the transverse bending test. Then, the analytical model is used to conducta parametric analysis on the effects of wire rope diameter, width, height, and number of turns (loops) on vertical stiffness. The wire ropediameter influences stiffness more than the other geometric parameters. The developed model can be accurately used for the evaluationand design of WRIs.

Simplified procedure for seismic demands assessment of structures

Benazouz Chikh,Youcef Mehani,Moussa Leblouba 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.3

Methods for the seismic demands evaluation of structures require iterative procedures. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformations and performance of structures. Recently, the concept of inelastic spectra has been adopted in the global scheme of the Performance-Based Seismic Design (PBSD) through Capacity- Spectrum Method (CSM). For instance, the Modal Pushover Analysis (MPA) has been proved to provide accurate results for inelastic buildings to a similar degree of accuracy than the Response Spectrum Analysis (RSA) in estimating peak response for elastic buildings. In this paper, a simplified nonlinear procedure for evaluation of the seismic demand of structures is proposed with its applicability to multi-degree-of-freedom (MDOF) systems. The basic concept is to write the equation of motion of (MDOF) system into series of normal modes based on an inelastic modal decomposition in terms of ductility factor. The accuracy of the proposed procedure is verified against the Nonlinear Time History Analysis (NL-THA) results and Uncoupled Modal Response History Analysis (UMRHA) of a 9-story steel building subjected to El-Centro 1940 (N/S) as a first application. The comparison shows that the new theoretical approach is capable to provide accurate peak response with those obtained when using the NL-THA analysis. After that, a simplified nonlinear spectral analysis is proposed and illustrated by examples in order to describe inelastic response spectra and to relate it to the capacity curve (Pushover curve) by a new parameter of control, called normalized yield strength coefficient (η). In the second application, the proposed procedure is verified against the NL-THA analysis results of two buildings for 80 selected real ground motions.

Behavioral trends of shear strengthened reinforced concrete beams with externally bonded fiber-reinforced polymer

Samer Barakat,Salah Altoubat,Moussa Leblouba,Eman Al Burai 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.5

Numerous experimental studies have been conducted on reinforced concrete (RC) beams strengthened in shear with externally bonded fiber reinforced polymer (EBFRP). The objectives of this work are to study the behavioral trends of shear strengthened EBFRP RC beams after updating the existing database. The previously published databases have been updated, enriched and cross checked for completeness, redundancy and consistency. The updated database now contains data on 698 EBFRP beams and covers the time span from 1992 to 2018. The collected database then refined applying certain filters and used to investigate and capture better interactions among various influencing parameters affecting the shear strength of EBFRP beams. These parameters include the type and properties of FRP, fiber orientation as well as the strengthening scheme, the shear and the longitudinal steel reinforcement ratios, the shear span ratio, and the geometry of the member. The refined database is used to test the prediction accuracy of the existing design models. Considerable scatters are found in the results of all tested prediction models and in many occasions the predictions are unsafe. To better understand the shear behavior of the EBFRP RC beams and then enhance the prediction models, it was concluded that focused experimental programs should be carried out.