Jamal A. Abdalla

Behavior of reinforced concrete beams strengthened with externally bonded hybrid fiber reinforced polymer systems

Abstract This paper presents an experimental and an analytical investigation of the behavior of Reinforced Concrete (RC) beams strengthened in flexure by means of different combinations of externally bonded hybrid Glass and Carbon Fiber Reinforced Polymer (GFRP/CFRP) sheets. In order to obtain the mechanical properties of the hybrid sheets, multiple tensile coupon tests were conducted. In addition, an experimental program consisting of a control beam and four beams strengthened in flexure with GFRP, CFRP and hybrid FRP sheets was conducted. The series of the RC beams were tested under four point bending to study the flexural effectiveness of the proposed hybrid FRP sheets. The load–deflection response, strain readings at certain locations and associated failure modes of the tested specimens had been recorded. It is observed that the increase in the load capacity of the strengthened beams ranged from 30% to 98% of the un-strengthened control RC beam depending on the combination of the Carbon/Glass sheets. It was also observed that the ductility at failure loads of the beams strengthened with glass and hybrid sheets is higher than that with a single carbon sheet. Hence, the selection of the optimum combination of hybrid sheets can lead to a strengthening material which provides an improved ductility and strength in beam behavior. The load carrying capacity of the tested specimens was then predicted by the ACI 440.2R-08 guidelines. The predicted and measured results were in good agreement, within 5% for the control beam and for beams with one layer of strengthening sheet and between 13% and 17% for beams with two or more layers of hybrid strengthening sheets. Furthermore, an analytical model was developed to predict the load–deflection response of the tested specimens and the results were compared with the measured experimental data. The results showed that the developed analytical model predicted the response of the tested beam specimens with reasonable accuracy.

Modeling and simulation of shear resistance of R/C beams using artificial neural network

Artificial neural network (ANN) has been used in several engineering application areas including civil engineering. The use of ANN to predict the behavior of reinforced concrete (R/C) members, using the vast amount of experimental data as a test-bed for learning and verification of results, proved to be a viable method for carrying out parametric studies. This paper presents application of ANN for predicting the shear resistance of rectangular R/C beams. Six parameters that influence the shear resistance of beams, mainly shear-span-to-depth ratio, concrete strength, longitudinal reinforcement, shear reinforcement, beam depth and beam width, are used as input for the ANN. A back propagation neural network (BPNN) with different activation functions is used and their results are compared. The sigmoid function with variable threshold is adopted due to its accuracy of prediction. The ANN prediction and the measured experimental values are compared with the shear strength predictions of ACI318-02 and BS8110 codes. A sensitivity study of the parameters that affect shear strength of R/C beams is carried out and the underlying complex nonlinear relationships among these parameters were investigated. Shear response curves and surfaces based on these parameters were generated. It is concluded that ANN can predict, to a great degree of accuracy, the shear resistance of rectangular R/C beams and it is a viable tool for carrying out parametric study of shear behavior of R/C beams.

SEISMIC HAZARD ASSESSMENT OF UNITED ARAB EMIRATES AND ITS SURROUNDINGS

This paper presents the seismic hazard assessment and seismic zoning of the United Arab Emirates (UAE) and its surroundings based on the probabilistic approach. The area that has been studied lies between 50°E-60°E and 20°N-30°N and spans several Gulf countries. First, the tectonics of the area and its surroundings is reviewed. An updated catalogue, containing both historical and instrumental events is used. Seismic source regions are modelled and relationships between earthquake magnitude and earthquake frequency is established. A modified attenuation relation for Zagros region is adopted. Seismic hazard assessment is then carried out for 20 km interval grid points. Seismic hazard maps of the studied area based on probable Peak Ground Acceleration (PGA) for 10% probability of exceedance for time-spans of 50, 100 and 200 years are shown. A seismic zone map is also shown for a 475-year return period. Although the results of the seismic hazard assessment indicated that UAE has moderate to low seismic hazard levels, nevertheless high seismic activities in the northern part of UAE warrant attention. The northern Emirates region is the most seismically active part of UAE. The PGA on bedrock in this region ranges between 0.22 g for a return period of 475 years to 0.38 g for a return period of 1900 years. This magnitude of PGA, together with amplification from local site effect, can cause structural damage to key structures and lifeline systems.

Modeling and simulation of low-cycle fatigue life of steel reinforcing bars using artificial neural network

This study presents a model for predicting the low-cycle fatigue life of steel reinforcing bars using Artificial Neural Network (ANN). A Radial Basis Function (RBF) artificial neural network topology with two additional hidden layers and four neurons (processing elements) in each of these layers is used. The input parameters for the network are the maximum tensile strain (e s,max ) and the strain ratio (R) and the output of the ANN is the number of cycles to fatigue failure (N f ). Low-cycle fatigue tests were conducted by the authors in a previous study for different types of steel reinforcing bars subjected to different strain amplitudes and at different strain ratios. The data resulted from these tests were used to train and test the ANN. It is observed that the ANN prediction of low-cycle fatigue life of steel reinforcing bars is within ±2 cycles of the experimental results for the majority of the test data. A parametric study had been carried out to investigate the effect of maximum strain and strain ratio on the fatigue life of steel reinforcing bars. It is concluded that both the strain ratio and the maximum strain have significant effect on the low-cycle fatigue life of such bars, especially at low values of maximum strain and their effect should be considered in both analysis and design. Other observations and conclusions were also drawn.

Probabilistic Seismic Hazard Assessment of Sudan and Its Vicinity

This paper presents seismic hazard assessment and seismic zoning of Sudan and its vicinity based on probabilistic approach. The area studied lies between 22° E-45° E and 0° - 24° N. Tectonics of Sudan and its vicinity is first reviewed. An updated NOAA catalogue, containing both historical and instrumental events and covering the period from 700 A.D. to 1993 is then used. Seismic source regions are modeled and relationships between earthquake magnitude and earthquake frequency are established. A modified attenuation relation is used. Seismic hazard assessment is then carried out for 60 km interval grid points. Seismic hazard maps of the studied area based on peak ground acceleration (PGA) for 10% probability of exceedance for time-spans of 50, 100, 200 and 250 years are presented. The results showed that the PGA ranges from 0.02g for low seismic activity regions to around 0.62g for high seismic activity regions. A seismic zone map is also shown for 475 years return period.

Probabilistic seismic hazard analysis and spectral accelerations for United Arab Emirates

In recent years, the United Arab Emirates (UAE) has experienced an unprecedented growth which is coupled with the increase in seismic activity in the surroundings. Previous studies presents significant variations in their results whereas some recent studies although very detailed focus on only few cities. This study reviews the results of previous studies and presents new findings for the whole of UAE based on the improved source model and use of next generation attenuation (NGA) equations. The peak ground accelerations, spectral accelerations and deaggregation of hazard for major cities are presented. Moreover, the breakdown of the range of mapped spectral accelerations (S0.2 and S1) is proposed to form the basis for the development of site amplification factors in subsequent studies. The results of this study indicate almost similar values of ground motion compared to some recently published studies and smaller values compared to some earlier studies.

Experimental investigation of bond-slip behavior of aluminum plates adhesively bonded to concrete

Abstract The main objective of this investigation is to assess the feasibility of using aluminum alloy (AA) plates as externally bonded strengthening material for reinforced concrete members. Consequently, the main aim of this paper is to experimentally investigate the bond stress-slip behavior of AA plates adhesively bonded to concrete surface. In addition, the effect of different AA surface roughness on the bond stress and bond behavior of AA-concrete interface was also investigated. Twelve specimens with six different surface roughnesses were instrumented and tested under single shear. The tested specimens have two bonded lengths – long bonded lengths (75% of prism length) and short bonded length (30% of prism length). It was observed that the bond shear stress, loading capacity, and failure modes vary with AA surface roughness and bonded length. The load capacity and maximum bond stress increased by 143.6 and 342.6%, respectively, for long bonded length (75%) of randomly grinded AA surface compared with those of normal AA surface. Such increase in load capacity and bond stress demonstrated the potential of using AA as externally bonded strengthening material. In addition, the bond-slip behavior of the AA plates was predicted, with reasonable level of accuracy, using existing bond-slip models that were originally developed for fiber-reinforced polymer materials. However, a more elaborate study is warranted to develop bond stress-slip models, specifically, for AA-concrete interface.

Artificial Neural Network Predictions of Fatigue Life of Steel Bars Based on Hysteretic Energy

AbstractThe fatigue life of steel reinforcing bars depends on the energy dissipated during cyclic loading. Steel bars play a major role in energy dissipation in reinforced concrete structures under low-cycle fatigue loading during earthquakes. In this study, seven artificial neural network (ANN) models were developed to predict the fatigue life of steel bars based on energy dissipated in the first cycle (W1), average cycles (WA), and total energy dissipated in all cycles (WT). The ANN-predicted number of reversals to fatigue failure (2Nf) were comparable to the experimentally measured values and also to the values predicted using nonlinear regression (NLR) models. The best overall ANN result was obtained when W1, WA, and WT were used together as input for the ANN with correlation coefficient r=0.985, normalized mean square error (NMSE)=0.0517, and mean absolute percent error (MAPE)=10.8%. When WA was used as a single input, the predicted 2Nf are also relatively accurate. In conclusion, the developed ANN m...

Retrofitting Pre-Cracked RC Beams Using CFRP and Epoxy Injections

The applications of Carbon Fiber Reinforced Polymers (CFRP) in construction have been grown drastically in the last 20 years because of the wide range of advantages and benefits of using CFRP in buildings, bridges and other type of structures. Nowadays, it is used for retrofitting concrete, masonry, steel and timber structures to resist both static and dynamic loads. Since the cost of replacing an existing structure is far more expensive than using FRP materials to strengthen it, CFRP strengthening techniques seem to be cost effective and easy to implement. Numerous experimental and numerical studies have been conducted to investigate the flexural and shear performance of uncracked reinforced concrete (RC) members externally strengthened with CFRP laminates or strips. However, the most practical usage of CFRP is to retrofit sections that had already been cracked and in need of maintenance. The fact that there have been limited studies to investigate the behavior and performance of pre-cracked beams strengthened with CFRP systems necessitated new and further investigations. In this study, the flexural performance of cracked RC beams retrofitted with CFRP plates and epoxy injections are investigated. The results of the cracked beams are compared with two control beams, a virgin un-strengthened beam and an uncracked beam strengthened with a CFRP plate covering 90% of the beam’s span. Load-midspan deflections for these beams were generated and compared. It is observed that the retrofitted cracked beams displayed more strength than the control beam. The results presented herein can aid designers in establishing a better understanding of the flexural performance of pre-cracked beams and how to economically retrofit such structural members.

Flexural Performance of Strengthened RC Beams with CFRP Laminates Subjected to Cyclic Loading

Seismic retrofitting of reinforced concrete (RC) beams by means of carbon fiber reinforced polymer (CFRP) composites is one of the state-of-the-art techniques that have been widely practiced lately. Such external strengthening schemes seem to enhance both stiffness and strength of RC beams when subjected to static and cyclic loading. Extensive research investigation has been carried out for beams subjected to monotonic static loading while limited research data is available for beams subjected to cyclic loadings. Therefore, this study is initiated and its aim is to present the results of full scale experimental testing of RC beams under four-point-bending loading and subjected to monotonic and cyclic loading histories up to failure of the specimens. An unstrengthened RC beam was tested monotonically to serve as a bench-mark. The remaining two externally strengthened RC beams with different anchorage schemes were tested under cyclic loading. The strengthening test matrix included beams bonded with a unidirectional CFRP plate that covers 90% of the beams soffit length, with one or two unidirectional layers of CFRP wraps at anchorage locations along the beams length. The anchorage locations were at the edges of the CFRP plate and at the middle of the beams span. The results presented herein show an increase in the overall strength for the strengthened beams over the unstrengthened ones. The different failure modes and the resulting ductility of the tested specimens are also discussed. This study is considered to be the first part of an extensive program that aims to investigate the different parameters that govern the external strengthening techniques of RC beams when subjected to cyclic loading.