Adil K. Al-Tamimi

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.

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.

Prediction of FRP-concrete ultimate bond strength using Artificial Neural Network

The ultimate bond strength between Fiber Reinforced Polymers (FRP) and concrete is one of the most important elements in the performance of the strengthened beam and its failure mode and failure mechanism. In this investigation an Artificial Neural Network (ANN) model has been developed to predict the ultimate bond strength (Pu) between FRP and concrete based on several factors that influence it. These factors, which were used as input to the ANN, include concrete prism width (bc), concrete compressive strength (fcu), concrete tensile strength (ft) as well as the FRP thickness (tf), width (bf), tensile strength (ff), elastic modulus (Ef) and the bond length (L) between FRP and concrete. The ANN predicted ultimate strength loads were compared with experimental values. It is concluded that the ultimate bond strength predicted by the ANN model are reasonably accurate compared to the experimental values and the accuracy can be further improved by using sufficient data generated by similar standardized tests. Based on the developed model, a parametric study can be carried out to investigate the influence of several parameters on the ultimate bond-strength between FRP and concrete and on the behaviour of bond slip compared to existing models.

Damage Evolution in Structural Steel at Different Loading Conditions

This paper presents an experimental and numerical characterization of ductile damage evolution in steel subjected to large plastic deformations. The main objective of this research is to better understand damage initiation and evolution in structural steel throughout the deformation process at different strain rates. The proposed study relies on a continuum damage mechanics approach that involves characteristic parameters to describe the accumulation of plastic strain, the damage variable, and the strain rates. The work was divided into experimental, and simulation phases. The experimental phase involved testing under monotonic uniaxial tensile loading under varying strain rates. The obtained material parameters are then used as the basic data in the simulations that are performed afterwards. Finally, this model was implemented as a new user defined material in the finite element analysis software ABAQUS where damage was quantified. Initial results of this research showed that a simple model with substantial cost and time saving can be developed for damage assessment in steel. The rate of loading is a main sensitive parameter that affects both damage initiation and propagation, as they increased significantly with increasing loading rate. Beyond the ultimate load, the strain energy was sufficient to cause the damage to increase without any further applied load.

EVALUATION OF FRP CONCRETE COMPRESSION MEMBER UNDER REPEATED LOAD AND HARSH ENVIRONMENT

Strengthening and rehabilitation have been increasingly applied in many structures to improve their capacity and serviceability. Fiber Reinforced Polymer (FRP) materials are universally known for their ability to improve the load capacity of damaged structural elements because of their high linear-elastic behavior. However, enhancing the capacity of structural elements that are exposed to repeated load coupled with harsh environment is an area that requires further investigation. This research focused on experimental analysis of the behavior and response of confined and unconfined concrete compression members (300mm x 150mm) under repeated load while exposed to 1440 cycles of seawater splash zone in United Arab Emirates (UAE). Confining concrete compression members with Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) sheets have increased the load capacity compared to the control sample at room temperature by 110% and 84%, respectively. Results showed that the average value of compressive strength for the confined concrete exposed to sea water splash zone conditions for CFRP and GFRP specimens has decreased by 33% and 23%, respectively, compared to the confined concrete in the room temperature. However, GFRP specimens showed higher performance in compressive strength under sea water splash zone than those of the CFRP specimens. Different mode of failures such as delamination, de- bonding and combination of such modes were observed and related to various exposure factors and mechanical properties.

Integrating Sustainability Education in a Classical Civil Engineering Program: The Case of Transportation and Construction Courses

Sustainability has emerged as a common theme in many processes related to urban life and the built environment. However, most engineering curricula still lacks the fundamentals of sustainable practices education that prepares graduating engineers to fulfill their expected roles and conduct future business in a more sustainable fashion. A more sustainable Civil Engineering curriculum requires a more systems approach to both diagnosing transport and built environment problems as well as devising solutions to such problems. This paper examines typical engineering curricula and identifies specific courses in the areas of transportation and construction where sustainability can be injected with minimum disruption to the structure of the course and/or its connection to other courses with the intended degree. For the two subspecialties, the core and elective courses are categorized and certain areas/modules within each course are identified, where the integration of sustainable engineering education is useful. Furthermore, some educational tools that facilitate the infusion of these concepts into the two subspecialties are presented.

Evaluation of the mechanical performance of short concrete column confined with CFRP and GFRP

Concrete has been successfully used to build strong and economic structures. However severe environmental exposures slowly deteriorate concrete strength until complete failure reducing its designed service life. Fiber Reinforced Polymer “FRP” has been recently introduced in the construction industry to strengthen and retrofitting several structural elements including columns. In this research two types of FRP have been used to wrap concrete column in order to increase its capacity; these are Carbon Fiber Reinforced Polymer “CFRP” and Glass Fiber Reinforced Polymer “GFRP”. Twelve short concrete columns have been wrapped with one and two FRP layers including CFRP and GFRP to evaluate their mechanical performance. Mechanical testing has shown that, in general, concrete columns wrapped with FRP produced higher modulus of elasticity compared to the control sample. Results showed that one layer of CFRP have 85.8% increases where as one layer of GFRP showed an increase of 64.5%. Furthermore, two layers of CFRP and GFRP showed 112.5% and 77.2% increase respectively.

Production of sustainable pavement with oil sludge

Oil sludge (OS) has been used as partial replacement of asphalt binder for road asphalt production. The properties of OS were studied and the results showed that it has high content of heavy oil. The oil removal from OS using the solvent extraction process showed the limitation of removing heavy oil content. The maximum removal of oil content was equal to 47%. This means that the remaining residue cannot be landfilled or disposed because of the high amount of heavy oil which contains heavy metals. OS was added to asphalt binder in specific amounts just to keep the properties of the final asphalt material within standard specification limits. Three percentages of OS to asphalt binder material were studied. Many tests were performed such as Marshall design experiment, penetration, flash point, softening point, stability and flow and loss of stability. The resultant tests of softening point, penetration point, stability, loss of stability, stiffness and flow showed the possibility of using 4% of this material as one of the materials of asphalt binder.

Evaluation of key performance financial perspectives on institutional facility management

Abstract This research utilizes Key Performance Indicators (KPIs) to assess facility management in a high educational institution. The analysis is compromised of 28 institutional buildings covering civil and structural work, electrical and mechanical systems, and safety access. It evaluates maintenance effectiveness, benchmarks the facility management, compares it to well known international institutions, and recommends measures required to improve its performance. Four perspectives of the balanced scorecard were utilized in this research; financial; internal business; growth; and customer satisfaction. Results show that the facility management lacks an effective strategic plan. The rating of the facility according to the balanced score card against average facility condition is Good to Fair in all areas but one rating Poor. It also showed a gap between APPA “The Association of Higher Education Facilities Officers” guidelines and the current facility on the deferred maintenance.