Mohammad AlHamaydeh

Shear characteristics of GFRP-reinforced concrete deep beams without web reinforcement

This article investigates the shear behavior of deep concrete beams reinforced with glass fiber reinforced polymer for flexure and without shear reinforcement. A total of 13 beams were tested under four-point loading until failure. Nine of which reinforced with glass fiber reinforced polymer bars and four with steel bars. The ultimate shear capacity along with the load–deformation relationship of all beams was studied. The effects of the shear span to depth ratio a/d, reinforcement ratio ρ, beam effective depth d, and concrete compressive strength on the ultimate shear capacity and mode of failure of all beams were also investigated. Results show that the stiffness of steel-reinforced concrete beams (slope of the ascending portion of load–deflection curve) is higher than that of beams reinforced with fiber-reinforced polymer bars as expected, due to the low axial stiffness of the fiber-reinforced polymer material. A slight variation in the ultimate shear capacity was noticed but no clear trend was observed. In addition, beams reinforced with fiber-reinforced polymer exhibited larger deformation at their ultimate failure load, after which a sudden failure occurred especially for beams having high shear capacity.

Multiple regression modeling of natural rubber seismic-isolation systems with supplemental viscous damping for near-field ground motion

AbstractThis work presents the development and implementation of the Multiple Regression Analysis (MRA) model to Seismic-Isolation (SI) systems consisting of Natural Rubber Bearings and Viscous Fluid Dampers subject to Near-Field (NF) earthquake ground motion. A model representing a realistic five-story base-isolated building is used. Several damper properties are used in creating an array of feasible combinations for the SI system. Two ensembles of seven NF earthquake records are utilized representing two seismic hazard levels. The key response parameters investigated are the Total Maximum Displacement, the Peak Damper Force and the Top Story Acceleration Ratio of the isolated structure compared to the fixed-base structure. Mathematical models for the key response parameters are established via MRA. The MRA models produced acceptable results with significantly less computation. This is demonstrated via a practical example of how the MRA models would be incorporated in the design process, especially at th...

Impact of lateral force-resisting system and design/construction practices on seismic performance and cost of tall buildings in Dubai, UAE

The local design and construction practices in the United Arab Emirates (UAE), together with Dubai’s unique rate of development, warrant special attention to the selection of Lateral Force-Resisting Systems (LFRS). This research proposes four different feasible solutions for the selection of the LFRS for tall buildings and quantifies the impact of these selections on seismic performance and cost. The systems considered are: Steel Special Moment-Resisting Frame (SMRF), Concrete SMRF, Steel Dual System (SMRF with Special Steel Plates Shear Wall, SPSW), and Concrete Dual System (SMRF with Special Concrete Shear Wall, SCSW). The LFRS selection is driven by seismic setup as well as the adopted design and construction practices in Dubai. It is found that the concrete design alternatives are consistently less expensive than their steel counterparts. The steel dual system is expected to have the least damage based on its relatively lesser interstory drifts. However, this preferred performance comes at a higher initial construction cost. Conversely, the steel SMRF system is expected to have the most damage and associated repair cost due to its excessive flexibility. The two concrete alternatives are expected to have relatively moderate damage and repair costs in addition to their lesser initial construction cost.

Optimal Control of Magnetorheological Fluid Dampers for Seismic Isolation of Structures

This paper presents the modeling and control of a magnetorheological (MR) damper, installed in Chevron configuration, at the base of a 20-story benchmark building. The building structural model is created using the commercial software package ETABS. The MR damper model is derived from Bouc-Wen hysteresis model which provides the critical nonlinear dynamics that best represents the MR damper under a wide range of operating conditions. System identification is used to derive a low-order nonlinear model that best mimics the nonlinear dynamics of the actual MR damper. Dynamic behavior of this low-order model is tested and validated over a range of inputs. The damper model has proven its validity to a high degree of accuracy against the nonlinear model. A Kalman filter is designed to best estimate the state of the structure-damper system for feedback implementation purposes. Using the estimated states, an LQG-based compensator is designed to control the MR damper under earthquake loads. To demonstrate the effectiveness of this control strategy, four historical earthquakes are applied to the structure. Controlled and uncontrolled floor accelerations and displacements at key locations are compared. Results of the optimally controlled model demonstrate superior performance in comparison to the uncontrolled model.

Nonlinear AutoRegressive eXogenous Artificial Neural Networks for predicting Buckling restrained braces force

This paper proposes a novel approach for modeling the nonlinear dynamic behavior of Buckling-Restrained Braces (BRBs). The proposed approach is based on a combination of two architectures of Artificial Neural Networks (ANN) namely, Nonlinear AutoRegressive eXogenous (NARX) ANN and feed forward back propagation (FFBP) ANN. The proposed model predicts (outputs) the brace force at a certain time from the brace deflection and its history and the history of the brace force. The data used in training and testing of the model is acquired from the experimental testing of four BRB specimens. The proposed model is trained on data from one specimen while tested against the rest to demonstrate its learning and generalization capability. Optimum values for various network parameters are selected empirically to obtain the best network performance. The results show that the prediction error for the peak response (maximum tensile/compressive force) lies within ±5% confidence interval for all cycles.

Impact of Seismicity on Performance and Cost of RC Shear Wall Buildings in Dubai, United Arab Emirates

AbstractUnfortunately, available probabilistic seismic hazard studies are reporting significantly varying estimates for seismicity of Dubai. Given Dubai’s rapid economic growth, it is crucial to as...

Nonlinear Finite-Element Analysis of Buckling Capacity of Pretwisted Steel Bars

AbstractThis paper presents finite-element (FE) analysis to study the axial load capacity of pretwisted steel bars of rectangular cross sections. The FE simulations are conducted using the commercial software ABAQUS. The FE simulations include bars of 20- and 30-mm width, 3- and 6-mm thicknesses, and three different lengths of 300, 400, and 500 mm. The bar ends are gripped and embedded in cylindrical slips. A set of twisting angles, ranging between 0 and 270° with an increment of 15°, is considered for each length. Geometric imperfections as well as actual elastic-plastic behaviors have been implemented in nonlinear FE models. The column strengths, load-shortening curves as well as failure modes, were predicted. The FE model is initially verified by comparing the buckling capacity and mode of the simulated straight bars with the experiments and the AISC code. The bars are then twisted beyond their elastic limit, unloaded to remove elastic recovery, and subjected to axial displacement. FE simulations showe...

Optimization of Support Structures for Offshore Wind Turbines Using Genetic Algorithm with Domain-Trimming

The powerful genetic algorithm optimization technique is augmented with an innovative “domain-trimming” modification. The resulting adaptive, high-performance technique is called Genetic Algorithm with Domain-Trimming (GADT). As a proof of concept, the GADT is applied to a widely used benchmark problem. The 10-dimensional truss optimization benchmark problem has well documented global and local minima. The GADT is shown to outperform several published solutions. Subsequently, the GADT is deployed onto three-dimensional structural design optimization for offshore wind turbine supporting structures. The design problem involves complex least-weight topology as well as member size optimizations. The GADT is applied to two popular design alternatives: tripod and quadropod jackets. The two versions of the optimization problem are nonlinearly constrained where the objective function is the material weight of the supporting truss. The considered design variables are the truss members end node coordinates, as well as the cross-sectional areas of the truss members, whereas the constraints are the maximum stresses in members and the maximum displacements of the nodes. These constraints are managed via dynamically modified, nonstationary penalty functions. The structures are subject to gravity, wind, wave, and earthquake loading conditions. The results show that the GADT method is superior in finding best discovered optimal solutions.

OPTIMIZATION OF SEISMIC ISOLATION SYSTEMS WITH VISCOUS FLUID DAMPERS USING GENETIC ALGORITHMS

Abstract. This paper presents evolutionary-based optimization procedure for designing natural rubber seismic isolation systems with viscous fluid dampers. The proposed technique is applied to the design of seismic isolation systems with viscous fluid dampers. A lumped-mass stick model representing a realistic five-story MDOF system with natural period of vibration ranging between 2.5 to 4.5 seconds. A suite of 24 Near-Field (NF) earthquake records representing different seismic hazard levels are utilized in the analysis and design. The damping coefficient (C), damping exponent (α) and fundamental natural period (T) are used as design variables for the seismic isolation system. The minimization of the key response parameter, the top story acceleration ratio (TSAR) of the isolated structure compared to an identical fixed base structure, is selected as the objective function in this optimization problem. The total maximum displacements (DTM), the peak damper force (PDF), as well as the maximum drift ratio (δmax) are presented as constraints in the optimization problem. In order to achieve global optimum performance [TSAR] while handling competing constraints [DTM, PDF, δmax], the presented GA-based technique is utilized. The commercial structural analysis software SAP2000 is utilized to perform the dynamic analysis for the MDOF system through direct Time-History Analysis (THA). The optimization algorithm is programmed in MATLAB and linked to SAP2000 through its OAPI feature. In agreement with conventional wisdom and sound engineering experience, it is found that combining low values of (C), highly nonlinear (α) [low values] with highly flexible rubber isolators [long T] produces the optimum performance.

Adaptive seismic isolation of structures using MR-fluid dampers

This paper presents the modeling and control of an MR damper installed between the ground and first floor of a 5-story base isolated building. The building structural model is derived from a benchmark structure model using ETABS. The MR damper model considered is derived from Bouc-Wen Hysteresis model proposed by Spenser et al [1], and several other authors. System identification technique is used to derive a simple 4th order nonlinear model that best approximates the dynamics of the actual MR damper. The dynamic behavior of this simple model is tested and validated over a wide range of inputs and proved to be very representative of the Bouc-Wen Hysteresis model. A Kalman filter is designed to best estimate the state of the structure-damper system for the purpose of feedback implementation. An LQG based controller is designed to control the MR damper under dynamic loads. The effectiveness of this control strategy over a wide range of historical earthquakes is demonstrated. Accelerations and drifts at all building floors are computed and plotted. The controlled and uncontrolled results are compared and significant improvement in the MR damper performance is demonstrated.