Publications

In this paper, experimental work has been reported to investigate the efficiency of fiber-reinforced cementitious matrix (FRCM) in enhancing the flexural capacity and deformational characteristics of reinforced concrete (RC) beams.The aim of the experimental work is to assess the parameters that contribute to such enhancement.Twelve RC beam specimens, 2500 mm long, 150 mm wide and 260 mm deep, were prepared with two different reinforcement ratios of: ρ s D12 = 0.72% and D16 =1.27% , representing under-reinforced beam sections.The strengthened beams utilized two FRCM types; namely carbon and polyparaphenylene benzobisoxazole (PBO) FRCM systems.The RC beam specimens were tested in flexure under four-point loading until failure.Two beams without FRCM strengthening were used as control specimens.Six beams were externally reinforced by one, two and three layers of carbon FRCM system.Four beams were strengthened with one and two layers of PBO FRCM system.From the experimental observations, a reasonable gain in flexural strength was achieved for both the FRCM systems.Results showed that the flexural capacity of carbon FRCM strengthened beams (FRCM stiffness = 1422 MPa) can be increased by 78% and of PBO FRCM counterparts (stiffness = 605 MPa) by 27.5% over that of their control (un-strengthened) specimens.

SYMBOLIC MATRIX STRUCTURAL ANALYSIS OF TRUSSES: STATIC AND DYNAMIC APPLICATIONS - 10th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering - 15-18 June 2025, Rhodes Island, Greece

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Fabric-reinforced cementitous matrix (FRCM) composites are usually applied on the concrete surface for the purpose of strengthening reinforced concrete structures. However, the efficiency of FRCM strengthening is notably affected by the bond between the FRCM system and concrete substrate. In view of that, the current paper presents the results of a preliminary experimental study carried out to investigate the bond characteristics between FRCM composites and concrete. Six number of specimens, each consisted of a 150-mm concrete cube with a double-shear connection to an FRCM system, were subjected to direct-shear loading test. The parameters investigated include (a) FRCM material (carbon, polyparaphenylene benzobisoxazole (PBO), and glass); and (b) Bond length (75 mm or 100 mm). The FRCM systems typically included a single layer of fabric with the associated mortar, and the bond width was uniformly taken as 100 mm. The test results revealed that the bond capacity is enhanced with an increase in the FRCM bonded length. The PBO-FRCM showed the highest bond capacity between FRCM composite and concrete substrate among the three systems. The modes of failure observed in carbon-, PBO-, and glass-FRCM bond tests are fabric delamination, FRCM mortar/concrete debonding, and fabric rapture, respectively. The PBOand glass-FRCM bond tests thus exhibited a more brittle behavior at failure than that of the carbon-FRCM counterpart.

The authors would like to acknowledge the fund received by the NPRP grant # NPRP 9-110-2-052 from Qatar National Research Fund (a member of Qatar Foundation). The findings of this study are solely the responsibility of the authors

Six concrete mixes with different proportions of various pozzolanic materials were investigated for the development of high-strength non-autoclaved aerated concrete (NAAC). Fly ash and slag were used as partial cement replacements in order to perform comparative studies on the effects of fly ash and slag on NAAC. Aluminium powder was used as an expanding agent to produce gas in the mixes. The compressive strength of each mix after 7 and 28 d of curing was determined. The microstructure of the pozzolanic cellular concrete was also investigated using scanning electron microscopy. The influence of the pozzolanic materials on the microstructural and macrostructural characteristics of the cellular concrete was assessed. A cement-based concrete mix, with pozzolanic materials as partial replacements of cement and sand, was thus developed for lightweight cellular concrete with a 28 d compressive strength exceeding 17 MPa. The developed foam concrete with relatively high strength is ideal for several structural and non-structural applications.

This study presents experimental and analytical investigations on the axial capacity of 12 heat-damaged glass fiber-reinforced polymer reinforced concrete columns. The columns were prepared with dimensions of 200×200×1000 mm and 3 replacement ratios of seawater for concrete mixing and curing (0%, 50%, and 100%). At the age of 3 months, the columns were subjected to an elevated temperature of 500 oC for 30, 60, and 90 minutes and subsequently cooled and tested. The experimental results demonstrated that the compressive strength of concrete increased by 35% and 45% at seawater replacement ratios of 50% and 100%, respectively. In addition, seawater-concrete mixes exhibited a lower rate of strength development compared to the reference mix. Moreover, 100% seawater concrete columns reported an increase of 28% in the cracking and ultimate loads. However, columns at seawater replacement ratios of 0%, 50%, and 100% exhibited a drop of 27%, 53%, and 50% in the cracking load after being exposed to 500 oC for 90 minutes. Additionally, the columns exposed to elevated temperatures showed a reduction of 5% to 20% in the ultimate load. Furthermore, the analytical models of ACI 440.11-22 and CAN/CSA-S806-12 significantly underestimated the axial capacity of all columns. The most accurate prediction for the columns' axial capacity was associated with the analytical model of Mohamed et al. with mean, standard deviation, and coefficient of variance of experimental-to-predicted ratios of 1.17, 0.12, and 9.98%, respectively.

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There is considerable investment in construction industry in Qatar for civil infrastructures and taking into account the severe environmental conditions, they would entail for proper maintenance, repair and strengthening for safe, continuous, uninterrupted, and efficient functionality. Reinforced concrete (RC) structural members, which constitute majority of construction works in Qatar, can be easily deteriorated by the deleterious effect of seawater exposure in the form of humidity or direct splashing for sea-level and offshore structures. Such deterioration can also be due to the exposure to extreme high temperatures, severe humidity and high chloride. All such environmental effect can significantly reduce the life-span of RC structures by up to 10-15 years. The cost of rehabilitation and strengthening is usually estimated in millions of dollars. Traditional methods of strengthening corrosion-damaged structures involve the replacement of the corroded bars and the substitution of deteriorated concrete layers with new concrete. Our study proposes an “optimum strengthening technique” for RC structures to mitigate the prevailing conditions of Qatar. This relatively new technique utilizes “textile-reinforced mortar (TRM)” to strengthen concrete beams. TRM systems consist of one or more layers of textiles made of carbon, glass, or Polyparaphenylene benzobisoxazole (PBO) grids that are sandwiched between layers of associated cementitious mortars. The cement-based mortar used in TRM acts as a barrier against chloride ions penetration thus protecting the main reinforcing bars from corrosion attack. Textiles' lightweight, high tensile strength, corrosion resistance, and ease of application make the strengthening system appealing. The potential of TRM for the repair and strengthening of concrete structures is not just the result of its physio-mechanical performance but also the ease and simplicity of installation that does not require any sophisticated equipment or retraining of the construction work. In addition, the compatibility between the mortar used and the concrete substrate is inherited since both materials have the cement as a common “base”. TRM systems, with their innovative features, ensure the endurance of the rehabilitation process and consequently the sustainability of the strengthened structure. Recently in the last few years, several research works in the USA and Europe in the field of TRM strengthening technique have been reported for masonry and concrete structural members. Majority of these works is limited to single type of textile (either carbon, PBO or glass) and on limited types of reinforcement levels. The work presented here compares two different types of TRM systems in the same domain, performed on three different levels of reinforcement ratios representing flexural deficient, lightly reinforced and typical under-reinforced beams. Experimental works were done to state the efficiency and effectiveness of textile reinforced mortar (TRM) in increasing the ductility and the flexural capacity of reinforced concrete (RC) beams. The aim of the experimental work was to investigate the parameters that contribute to the increase in the load carrying capacity of beams strengthened with TRM system. Eighteen medium-scale rectangular RC beam specimens, 2500 mm long, 150 mm wide and 260 mm deep, were prepared at three different reinforcement ratios of “ “ρ” _“s” ^“1” “ = 0.5%;” o “ρ” _“s” ^“2” “ = 0.72%;” f: “ρ” _“s” ^“1” “ = 0.5%; “ “ρ” _“s” ^“2” “ = 0.72%; “ “ρ” _“s” ^“3” “ = 1.27%.” The strengthened beams utilized two TRM types namely carbon and Polyparaphenylene benzobisoxazole (PBO) TRM systems respectively. The RC beam specimens were tested in flexure under four point loading until failure with a clear span of 2.2 m. The strengthening technique was applied to the soffit of the beam (flat type) altering the number of layers of textile. Three beams (of three different reinforcement ratios) without TRM strengthening were used as control specimens. Nine beams were externally reinforced by one (“ρ” _“T-c” ^“1” “ = 0.014%”), two (“ρ” _“T-c” ^“2” “ = 0.028%”) and three (“ρ” _“T-c” ^“3” “ = 0.041%”) layers of carbon TRM system. Six beams were strengthened with one (“ρ” _“T-PBO” ^“1” “ = 0.009%”) and two (“ρ” _“T-PBO” ^“2” “ = 0.018%”) layers of PBO TRM system. From Based on the experimental observations, a reasonable gain in flexural strength and energy absorption was achieved for both the TRM systems. An increase of the initial stiffness was achieved for strengthened specimens; however, an apparent decrease in the overall ductility was observed with TRM strengthening. Results showed that the flexural capacity of strengthened beams increased to an average of 38% for carbon TRM system and an average of 26.7% for PBO TRM system over that of their control (un-strengthened) specimens. The highest increase in the load carrying capacity was 77.51% for a specimen having with the main reinforcement ratio of D12 (“ρ” _“s” ^“2” “ = 0.72%)” and was strengthened with carbon TRM system using three layers of carbon textile. Ductility index (ΔI) and energy absorption (Ψ) values were also calculated in order to know the behavior of ductility and flexural capacity in each of the beam specimen. The term ductility index (ΔI) is defined as the ratio between the deflection at the ultimate load and that at yield load, representing its ability to stretch/deform under sustained load before fracture. During experimentation, it was observed that the average values of ductility indices of using carbon as strengthening material were 1.1 × , 1.2 × and 0.5 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” beam specimens respectively to that of their control specimen. Similarly the average values of ductility indices of using PBO as strengthening material were 2.42 × , 0.75 × and 0.56 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” specimens respectively to that of the control specimen. Also the term energy absorption (Ψ) is defined as the area under the load- deflection curve up to the ultimate load, representing the amount of energy absorbed by the specimen before complete failure. The average values of energy absorption for using carbon as strengthening material were 1.8 × , 1.2 × and 1.6 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” beam specimens respectively to that of the control specimen. Similarly the average values of energy absorption for using PBO as strengthening material were 2.0 × , 1.0 × and 1.5 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and” “ρ” _“s” ^“3” “ = 1.27%” specimens respectively to that of the control specimen. Therefore, both the adopted TRM systems performed exceptionally well within the scope of the work, with carbon TRM system showing a relatively higher increase in the capacity of strengthened specimens and PBO TRM systems exhibiting relatively more ductile failure with higher bond strength between the TRM surface and concrete substrate. Moreover, crack patterns for the strengthened beam showed effective distribution of cracks/damage over the length of beam as compared to severe and concentrated damage in the associated control un-strengthened beams. Further, during the experimentation, it was seen that the technique of applying the TRM system also considers the contractor's ease where the construction workers (although not very skilled) can easily implement the technique after being given simple demonstrations. The study puts forth proper procedures and standards to the construction industry on the rehabilitation and strengthening of the existing concrete structures using innovative TRM strengthening technique. Successful implementation of the project will result in “state-of-the-art recommendations for design and construction specifications”, which will place Qatar and research at Qatar University in a leadership position not only limited to the Gulf region. Furthermore, this can potentially act as an “important initiation for the development of new industrial opportunities” in the country. Keywords Reinforced concrete beams, textile reinforced mortar, flexural strengthening, ductility index, energy absorption.

Background: While improved student engagement has been highlighted as an essential goal and a major outcome of Problem and Project-Based learning (PBL), little empirical evidence has been provided regarding types and forms of student engagement. Material and method: The study explored forms of student engagement in PBL settings, drawing on empirical data of observations and group interviews with 23 project teams (116 students) in four different PBL undergraduate civil engineering courses at Qatar University. Results: The study identified four patterns of student engagement in a PBL setting. Participants reported significant indicators of the first two patterns - engagement as autonomy and as connection. Regarding the other two indicators, namely relational and emotional engagement, they reported positive yet slightly fewer indicators. Three factors were identified that influenced student engagement in a project teams, namely PBL types and its appropriateness to the nature of the course, students' prior experiences with PBL, and team dynamics. Conclusions: These results facilitate the establishment of an institutional framework supporting a progressive approach to embracing PBL. In this framework PBL implementation begins with diverse practices at the course level and has systemic change as its ultimate goal. This framework particularly aims to support an institutionalized approach to transition to PBL in a socio-cultural context (e.g., a non-western context) where instructors are as the primary and authoritative source of knowledge. The overall outcome of the study supports management of change from a lecture-based mode to PBL in a non-western context.

This study focuses on the evaluation of the surface deformation height of ribbed type of GFRP rebars. The bond behaviour of ribbed type of GFRP rebar is investigated in terms of the effective deformation height and bond rigidity, both experimentally and numerically. Pullout tests on ribbed type GFRP rebars embedded in concrete have been conducted to obtain an accurate bond stress-slip law and also to closely observe the state of the surface of pulled-out rebars at failure, in order to categorise accurately the mode of failure. In the pullout tests, the high temperature regime is particularly considered. In addition, finite element (FE) simulations of the specimens subjected to pullout tests are developed. From the FE analyses and the experiments, the effective surface deformation height and bond rigidity of the GFRP rebar with ribs was determined. The numerical results were substantiated by the experimental findings and good agreement was observed. Moreover, adding milled glass fibres in the surface deformations could not increase the effective surface deformation height and bond rigidity of the rebar; however, it seems to improve the bond strength because increasing the proportion of milled glass fibres improves the connections between the core and rib section.

It has been demonstrated, through laboratory investigations and various field projects, that the external bonding of fiber- reinforced polymer (FRP) laminates is an effective technique for the structural enhancement of reinforced concrete slabs. In such applications, failure is generally governed by debonding of the FRP laminate. Nevertheless, numerical simulations to date of FRP-strengthened slabs have usually been based on the assumption of full bond between the concrete and FRP. In this study, the interfacial behavior between the FRP laminates and the concrete substrate is accounted for by introducing appropriate bond-slip models for the interface in a nonlinear finite-element analysis of FRP-strengthened two-way slabs. The numerical model is capable of simulating slabs strengthened in shear or in flexure; it can be applied to arbitrary FRP configurations, and can also accommodate both passive as well as prestressed FRP strengthening schemes. Results are presented in terms of load-deflection relationships, ultimate load capacities, failure modes, and interfacial slip and stress distributions. When compared to test results reported in the literature, the analysis is shown to lead to excellent predictions in that, for the entire set of FRP-strengthened specimens considered, the average of the numerical-to-experimental load capacity ratios is 0.966, with a standard deviation of 0.066. Furthermore, in all cases when FRP debonding was observed experimentally, the analysis correctly predicted the mode of failure.

Fiber-reinforced polymer (FRP) composites have become popularly utilized in structural engineering applications.The common use of the FRP composites is related to their economic benefits that can be observed right away or in a long-time period.With increasing concern about global warming and the shortage of natural resources, it is essential to study the environmental implications of the use of FRP composites.Life cycle assessment (LCA) is one of the most common techniques that can be used to take the environmental impact of the FRP into consideration.This paper presents a literature review about the LCA of FRP composites in concrete beams.The LCA results reported in the literature confirmed the use of FRP composites for reinforcing the RC beams instead of conventional steel rebars or that the strengthening of RC beams instead of demolishing and reconstruction is a more environment-friendly approach.

This paper constitutes a special importance for developing countries where an affordable trowel-based strengthening system is needed. This paper also provides an affordable strengthening solution when it is not possible to entirely remove the effect of live load on the strengthened element. A series of 13 ferrocement strengthened beams of 2,400 mm in length and a rectangular cross section of 120×200 mm were tested. The beams were cast and preloaded to different load fractions (45 and 60%) of its ultimate capacity; then the load was partially released (by 15% of the ultimate load) and maintained, while the beams were then strengthened and reloaded until failure. The load released simulates the removed live load while strengthening an actual beam. The research reported in this paper features designing and manufacturing a special loading frame to apply, release, and reapply the loads on the tested beams. The frame allows implementing the strengthening process while maintaining the strengthened beams partially loaded. The use of flat and U-shaped ferrocement layers of three different volume fractions (VFs) of mesh reinforcement have been assessed. The overall response of the specimens was investigated in terms of the load carrying capacity, crack patterns, and propagation and modes of failure, and the deformational characteristics that include deflection, ductility, and energy absorption characteristics. The results indicated that the ferrocement strengthening system is effective in enhancing both strength and ductility of the RC beams.