Structural behaviour of CFRP strengthened beam-column connections under monotonic and cyclic loading

Welded beam-column connections may be vulnerable to failure under cyclic loading conditions. These connections might require strengthening to resist static and cyclic loads as they may exhibit inadequate capacity due to the design errors or material properties degradation because of severe environmental effects or an increase in service loads. With this in mind, a series of full-scale experiments have been conducted to investigate the behaviour of the bare and strengthened welded beam-column connections under both monotonic and large-displacement cyclic loading. Carbon fibre reinforced polymer (CFRP) is used as the strengthening material in the present study along with epoxy adhesive as the bonding material. The experimental study conclusively showed the benefits of CFRP composites to improve the performance of welded connections under both monotonic and cyclic loadings. Under monotonic loading, the ultimate moment capacity, stiffness, dissipation of energy and ductility of the welded connections improved by strengthening with CFRP. Additionally, under cyclic loading, the CFRP strengthened welded connections showed improvement in moment hysteresis behaviour, higher stiffness and energy dissipation capacity compared to their bare counterparts. Moreover, the experimentally obtained moment capacities match reasonably well with the theoretically predicted moment capacities

Performance of FRP strengthened full-scale simply-supported circular hollow steel members under monotonic and large-displacement cyclic loading

Steel structures are becoming more common in engineering construction as steel possesses excellent ductility, but steel members are often vulnerable to buckling, especially under seismic or cyclic loading. Hollow structural sections (HSS) often buckle locally under loading due to their thin steel walls and the need for rehabilitation and strengthening is increasing. In the present study, circular hollow section (CHS) steel members have been strengthened with both carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). Their structural performance, along with that of their bare counterparts, is investigated subjected to monotonic and quasi-static large-displacement cyclic loading experimentally. The types of FRP reinforcement (CFRP and GFRP) and the loading condition (monotonic and cyclic) are chosen as two main parameters in the test program. Results reveal the significant structural improvements of the strengthened CHS members under monotonic and cyclic loading. The ultimate moment capacities of the beams under monotonic and cyclic loading are enhanced by 51.0% and 35.4% respectively with CRFP strengthening and 43.3% and 31.5% respectively with GFRP strengthening compared to the bare beam. In addition, all the FRP strengthened specimens achieved higher moment capacities, rotational capacities, stiffness, energy dissipation capacities and ductility in comparison to their bare counterparts. Moreover, there is a good agreement found between the experimental and theoretically predicted ultimate moment capacities of the bare and strengthened CHSs with a mean ratio of 1.04 and a COV of 0.05

Developing machine learning model to estimate the shear capacity for RC beams with stirrups using standard building codes

Shear failure in reinforced concrete (RC) beams with a brittle nature is a serious safety concern. Due to the inadequate description of the phenomenology of shear resistance (the shear behavior of RC beams), several of the existing shear design equations for RC beams with stirrups have high uncertainty. Therefore, the predicted models with higher accuracy and lower variability are critical for the shear design of RC beams with stirrups. To predict the ultimate shear strength of RC beams with stirrups, machine learning (ML)-based models are proposed in the present research. The models were created using a database of 201 experimental RC beams with stirrups gathered from earlier investigations for training and testing of the ML method, with 70% of the data being used for model training and the rest for testing. The performance of suggested models was evaluated using statistical comparisons between experimental results and state-of-the-art current shear design models (ACI 318–08, Canadian code, GB 510010–2010, NZS 3101, BNBC 2015). The suggested machine learning-based models are consistent with experimentally observed shear strength and current predictive models, but they are more accurate and impartial. To understand the model very well, sensitivity analysis is determining as input values for a specific variable affect the outcomes of a mathematical model. To compare the results with different machine learning models in training and testing R2 , RMSE and MSE are also established. Finally, proposed ML models such as gradient boost regressor and random forest give higher accuracy to evaluate the shear strength of the reinforcement concrete beam using stirrups.Md Nasir Uddin, Kequan Yu, Ling, zhi Li, Junhong Ye, T. Tafsirojjaman, Wael Alhadda

Effect of Hydrothermal Environment on Mechanical Properties and Electrical Response Behavior of Continuous Carbon Fiber/Epoxy Composite Plates

In this work, the effect of a hydrothermal environment on mechanical properties and the electrical response behavior of continuous carbon fiber/epoxy (CFRE) composite produced by the pultrusion method were investigated. Due to the relatively uniform distribution of fibers and lack of resin-rich interlayer area, this effect for the pultruded CFRE composite plates is different from the common CFRE laminated composites. Firstly, its hygroscopicity behavior was studied. The absorption ratio increases rapidly to 1.02% within 3 days before reaching a relatively stable state. A three-point bending test, a Vickers hardness test, a thermogravimetric analysis (TGA), and a scanning electron microscope (SEM) analysis were performed to investigate the effect of the hydrothermal environment on the mechanical properties and thermal stability of the CFRE composite. The results indicated that the bending strength decreased quickly within 3 days of hydrothermal treatment, followed by a stable trend, which coincided with that of the hygroscopicity behavior of the composites. The fracture surface analysis indicated that the interfacial properties of carbon fibers in the epoxy matrix were decreased after the hydrothermal treatment, and more carbon fibers could be pulled out from the CFRE in the hygroscopic state. After the hydrothermal treatment, the micro-hardness of the composites was reduced by 25%. TGA confirmed the decreased thermal stability of the CFRE composites after the hydrothermal treatment as well. Moreover, the hydrothermally treated CFRE composites could a reach stable resistance response more readily. The revealing of the effect of moisture and hot environment on the mechanical properties and electrical response behavior of pultruded CFRE composites prepares the ground for their design and practical application in the corresponding environment.Runtian Zhu, Xiaolu Li, Cankun Wu, Longji Du, Xusheng Du, and T. Tafsirojjama

Analysis of failure modes in pipe-in-pipe repair systems for water and gas pipelines

Different failure modes should be carefully analyzed to effectively design the pipe-in-pipe (PIP) repair systems to rehabilitate natural gas and water pipelines in place and in service. This study characterizes the failure modes through analytical and numerical modelling of the different performance objectives to have a comprehensive understanding of the overall behavior of PIP systems with a range of thicknesses and elastic moduli. It focused on assessing the structural performance of PIP systems under different load actions including vibration/fatigue due to traffic loads, lateral deformation, cross-section ovalization, axial stresses and thermal deformation, internal pressure, and impact. The results of the analyses showed that the thickness and elastic modulus significantly affect the failure modes of PIP systems. The implemented Analytical Hierarchy Process (AHP) suggested that lateral deformation is the most critical failure mode followed by internal pressure based on global priority as well as both criteria (thickness and elastic modulus) when the design pressure is 200 psi with the cross-section ovalization the least critical failure mode of the PIP systems. The results of this study provide useful predictive modelling techniques and preliminary design tools for PIP systems for new material systems development and/or evaluation of the suitability of the available PIP systems for pipeline repair.T. Tafsirojjaman, Allan Manalo, Cam Minh Tri Tien, Brad P. Wham, Ahmad Salah, Shanika Kiriella, Warna Karunasena, Patrick Dixo

Development of a Testing and Analysis Framework for Validation of Rehabilitating Pipe-in-Pipe Technologies

Aging natural gas pipeline infrastructure needs rehabilitation, and trenchless, pipe-in-pipe (PIP) technologies offer a versatile solution. For example, legacy cast/wrought iron pipes have been subject to elevated incident rates for decades (www.phmsa.dot.gov). In an effort to accelerate innovation, the United States (U.S.) Department of Energy (DOE) has invested in a recently initiated, 3-year research program focused on pipeline “REPAIR”. To establish industry adoption of new technologies, a robust framework to evaluate and validate systems under in-service loading conditions is required. This paper introduces the approach taken by the Testing and Analysis team to develop a framework that confirms a 50-year design life for the PIP technologies. Testing protocols involve a comprehensive literature review, performance criteria, and relevant load cases and failure modes of PIP technologies. We use numerical and analytical modelling to investigate failure modes and severe conditions, thus informing testing protocols. In this paper, we discuss analytical frameworks and proposed model validation methods. We further discuss plans for test geometries (e.g., circumferentially cracked host pipe) and protocols (e.g., cyclic/dynamic traffic loading) to apply relevant load cases and probe failure modes in service. Modifications and enhancements are investigated in light of the insights gained from review and modelling. The testing and analysis framework for validating service life performance of trenchless PIP repair methods is intended to accelerate the development and adoption of new and safe repair technologies in the gas industry, as well as other critical lifeline systems.Patrick G. Dixon, Brad P. Wham, Jacob Klingaman, Allan Manalo, T. Tafsirojjaman, Khalid Farrag, Thomas D. O, Rourke, Mija H. Hubler, Shideh Dasht

Investigation on the behaviour of CFRP strengthened CHS members under monotonic loading through finite element modelling

During the past several years, civil infrastructure has made extensive use of tubular hollow steel members as structural elements. However, the rehabilitation and strengthening of tubular hollow steel members is a major concern due to design errors, environmental effects, reduction in material properties over time caused by corrosion and the need to withstand increased loads. A comprehensive investigation on the strengthening of tubular hollow steel members is therefore required. Although carbon fibre reinforced polymer (CFRP) strengthening technique has shown its effectiveness to improve the structural response of different steel members, studies on the structural response of circular hollow section (CHS) steel members strengthened with CFRP is limited. In the present study, an effective finite element (FE) model is first developed by comparing the FE model simulated results with the authors' experimental results. This is followed by a parametric study on the effect of the bond length of CFRP, number of CFRP layers, ratio of CFRP thickness to CHS wall thickness, diameter to thickness ratio of CHS and steel grade of CHS on the structural behaviour of the strengthened member subjected to monotonic loading. These parameters had noteworthy effects on the behaviour of the CFRP strengthened CHS steel members under monotonic loading. The CFRP strengthened CHS steel members showed an improvement in the moment capacity, secant stiffness, energy dissipation capacity and ductility compared to their bare CHS steel members. It can be concluded that the effectiveness of the CFRP strengthening technique is enhanced with the increase in the ratio of CFRP thickness to CHS wall thickness and/or increasing the diameter to thickness ratio of CHS. In contrast, the effectiveness of the CFRP strengthening technique is decreasing with the increasing of the steel grade

Enhancement of Seismic Performance of Steel Frame through CFRP Strengthening

Seismic strengthening is an urgent need for mitigating the high collapse risk of existing and future constructed steel frames during the possible earthquakes in the future. In this study steel frames are strengthened by using externally bonded carbon fibre reinforced polymers (CFRP) composites with varying the layers number of CFRP to mitigate the seismic action on steel frames. Shake table test of bare and strengthened steel frames has been performed. The CFRP strengthening technique improved the stiffness of the steel frames which results less lateral deflection of the steel frames under seismic action and indicates its effectiveness for seismic mitigation of steel frames

Experimental Research on Bonded Anchorage of Carbon Fiber Reinforced Polymer Prestressed Strands

Aiming at the problems of a large number of corrosion and fatigue damage of the current prestressed steel strands, this paper adopts carbon fiber-reinforced composite (CFRP) strand with better corrosion resistance and fatigue resistance and uses it in concrete structures. The bond anchorage is usually used to anchor CFRP tension members, which bonds the CFRP through the binding medium. Through experimental research on the CFRP strand bond anchorage, the inner taper of the CFRP prestressed strand cone was anchored and the influence of different anchor lengths and bonding media on the anchorage performance was determined. The test results demonstrate that the taper of the conical anchorage described in this paper is a key factor affecting its anchorage performance and increasing the inner taper within a certain range is beneficial to improving the anchorage performance of the conical anchorage. The bonded anchorage of the CFRP prestressed strand with a 200 mm anchor is the most reliable and efficient, as the taper of the 200 mm anchor is the largest. The average anchoring efficiency coefficient of the 200 mm anchor was 96.4%, which is 3.7% and 2.6% higher than the average anchoring efficiency coefficient of 220 mm and 250 mm anchors, respectively. The anchoring efficiency of the anchor is also high (94.1%) when the epoxy resin mortar is used as the bonding medium. Moreover, after an appropriate amount of quartz sand is added to the epoxy resin, the overall comprehensive performance of the anchor can be improved to a certain extent and the stress of the CFRP strand can be improved. The coupling between ultra-high-performance concrete dry mix (UHPC-GJL) and CFRP strand materials is not suitable for UHPC-GJL being used, as its binding medium as the average anchoring efficiency coefficient is only 44.5% when UHPC-GJL is used as the anchor bonding medium

Experimental Research on Bonded Anchorage of Carbon Fiber Reinforced Polymer Prestressed Strands

Aiming at the problems of a large number of corrosion and fatigue damage of the current prestressed steel strands, this paper adopts carbon fiber-reinforced composite (CFRP) strand with better corrosion resistance and fatigue resistance and uses it in concrete structures. The bond anchorage is usually used to anchor CFRP tension members, which bonds the CFRP through the binding medium. Through experimental research on the CFRP strand bond anchorage, the inner taper of the CFRP prestressed strand cone was anchored and the influence of different anchor lengths and bonding media on the anchorage performance was determined. The test results demonstrate that the taper of the conical anchorage described in this paper is a key factor affecting its anchorage performance and increasing the inner taper within a certain range is beneficial to improving the anchorage performance of the conical anchorage. The bonded anchorage of the CFRP prestressed strand with a 200 mm anchor is the most reliable and efficient, as the taper of the 200 mm anchor is the largest. The average anchoring efficiency coefficient of the 200 mm anchor was 96.4%, which is 3.7% and 2.6% higher than the average anchoring efficiency coefficient of 220 mm and 250 mm anchors, respectively. The anchoring efficiency of the anchor is also high (94.1%) when the epoxy resin mortar is used as the bonding medium. Moreover, after an appropriate amount of quartz sand is added to the epoxy resin, the overall comprehensive performance of the anchor can be improved to a certain extent and the stress of the CFRP strand can be improved. The coupling between ultra-high-performance concrete dry mix (UHPC-GJL) and CFRP strand materials is not suitable for UHPC-GJL being used, as its binding medium as the average anchoring efficiency coefficient is only 44.5% when UHPC-GJL is used as the anchor bonding medium.Liqiang Jia, Bo Wang, and T. Tafsirojjama