A hybrid reinforcement system is proposed which consists of a low modulus polymeric reinforcement combined with CFRP, and which is believed to overcome the lack of ductility in FRP reinforced concrete members. Three 4.2 m long and 400 mm deep, high strength concrete inverted T-beams were designed using this new concept and were tested under four point bending. Two of the beams contained hybrid reinforcement while the third contained only CFRP reinforcement (control beam). The control beam failed suddenly, following the rupture of the CFRP reinforcement. The beams with hybrid reinforcement failed in a ductile manner at 63% higher load and they had at least three times more deflection at failure than the control beam. In the later beams, deflections substantially increased following the rupture of CFRP, but the moment of resistance of the beams decreased marginally. Upon release of the load, the hybrid reinforced beams rebounded and had very little deflection under self-weight.
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This paper presents detailed analysis of the results of field tests on 13 full scale wide flange steel beams subjected to blast loads generated by the detonation of up to 250kg of ANFO explosive. The experimental results are analyzed using an equivalent Single-Degree-of-Freedom (SDOF) model of a beam, which includes material nonlinearity and strain rate effects. To account for strain rate effect on beam stiffness and strength, its full moment-curvature response is determined by dividing its cross-section into a number of layers and a strain rate-dependent stress-strain relationship, based on the Cowper–Symonds strain rate model, is used to capture the nonlinear stress distribution over the section. To determine the effects of higher modes of vibration and the variation of beam mechanical properties along its length on its dynamic response, the test beams are also analyzed using a Multi-Degree-of-Freedom (MDOF) model involving beam finite elements. Each element has two nodes and three degrees of freedom and is again divided into a number of layers to capture the strain rate effect and nonlinear stress distribution over its depth. The predicted displacements and strains by the two models are compared with the corresponding experimental data and the results show that for the given beams, the time-dependant deformations, internal forces, and moments can be adequately predicted by either model because the first mode of vibration is found to dominate their response; however, the use of a constant strain rate through the so-called Dynamic Increase Factor (DIF) can lead to highly conservative estimate of the actual strength of such members.
The authors are to be congratulated for their comprehensive research work on the use of RCA as aggregate in structural grade concrete [1], but some of their conclusions with regard to the effect of aggregate type and RCA content on the fresh and hardened properties of concrete made with coarse RCA, termed RAC for brevity, need discussion.
A new type of wall for building envelope is studied and its performance is analyzed in detail using computational fluid dynamics. The wall is designed to absorb and store passive solar energy during the day in winter and release it to the inside of the building at night. The salient feature of the wall is the presence of a phase change material (PCM) layer within the wall and its ability to switch its position with the insulation layer within the wall. During the day, the PCM layer is sandwiched between the outer brick layer and the insulation while after sunset the PCM swaps position with the insulation. The thermal performance of the proposed wall is compared with those of two analogous walls, one without PCM and the other with a similar static PCM layer. Results show the superior thermal performance of the proposed wall vis-à-vis the other two walls as it could save up to 89% of the energy normally used to heat the adjoining conditioned space during a severely cold winter. Moreover, this saving is realized by using only 0.32 kg of PCM per cubic meter of conditioned space, which is 50% less than previously used by other investigators.
The behavior of reinforced concrete panels, or slabs, retrofitted with glass fiber reinforced polymer (GFRP) composite, and subjected to blast load is investigated. Eight 1000×1000×70mm panels were made of 40MPa concrete and reinforced with top and bottom steel meshes. Five of the panels were used as control while the remaining four were retrofitted with adhesively bonded 500mm wide GFRP laminate strips on both faces, one in each direction parallel to the panel edges. The panels were subjected to blast loads generated by the detonation of either 22.4kg or 33.4kg ANFO explosive charge located at a 3-m standoff. Blast wave characteristics, including incident and reflected pressures and impulses, as well as panel central deflection and strain in steel and on concrete/FRP surfaces were measured. The post-blast damage and mode of failure of each panel was observed, and those panels that were not completely damaged by the blast were subsequently statically tested to find their residual strength. It was determined that overall the GFRP retrofitted panels performed better than the companion control panels while one retrofitted panel experienced severe damage and could not be tested statically after the blast. The latter finding is consistent with previous reports which have shown that at relatively close range the blast pressure due to nominally similar charges and standoff distance can vary significantly, thus producing different levels of damage.
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The generalized Vlasov's thin-walled beam theory was combined with the finite element technique to develop a new curved thin-walled multicell box girder finite element which can model extension, flexure, torsion, torsional warping, distortion, distortional warping and shear lag effects. For multicell box girders, several distortional modes are introduced to describe the complete distortional behavior of the cross-section. The element is one dimensional, it has three nodes and employs the conventional polynomial shape functions. For modeling flexure, Timoshenko's beam theory is used to take account of shear deformations.
One of the most urgent problems related to highway infrastructure is that the cost of maintaining a network of bridges with an acceptable level of service is more than the available budgeted funds. Low prioritization of the available resources allocated to bridge projects exacerbates the situation. About 42 percent of the 574,000 highway bridges in the United States were reported by FHWA to be structurally deficient or functionally obsolete. Traditional management practices have become inadequate as ways to face this serious problem. Priority-setting schemes for bridge projects range from those done on a subjective basis in which engineering judgment is used to those that use very complex optimization models. However, currently used priority-setting schemes do not have the ability to optimize the system's benefits to obtain optimal solutions. The present objective is to show how artificial neural networks (ANNs) can be used to optimize the system's resources to generate the group of bridge improvements that minimizes the loss of the network benefits. ANNs are algorithms with characteristics that are able to solve certain classes of optimization problems. The advantages of using ANNs include improvements in the speed of operation by parallel implementation either in hardware or in software. It is also possible to implement ANNs by optical devices that operate at higher speeds than traditional electronic chips.
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Membrane scaling is unavoidable when treating highly concentrated and even supersaturated brine in the continuous membrane distillation (MD) process. Omniphobic membranes with higher nucleation energy barriers could partially mitigate the membrane scaling. Herein, we fabricated omniphobic corrugated membranes to further alleviate membrane scaling via the synergistic effects of omniphobicity and corrugation on the membrane surface. The scaling behaviors of omniphobic flat membrane (#PVDF-FF), omniphobic corrugated membrane (#PVDF-CF) at parallel (PL) and perpendicular (PD) modes were investigated. Different modes represented the relative position between the feed flow direction and the pattern of corrugated membrane. The results showed that the modified corrugated membranes had water contact angles over 150° and anti-wettability against low surface tension liquids. Compared to #PVDF-FF, #PVDF-CF at the PL mode exhibited a better slippery property while the PD-mode #PVDF-CF had higher slippery resistance. The membrane omniphobicity was confirmed to be effective against membrane scaling when treating a 3.5 wt% NaCl feed solution. However, the scaling resistance of #PVDF-CF at both PL and PD modes was much better than that of #PVDF-FF when 25 wt% NaCl or 20 mM supersaturated gypsum solutions were used as feeds. The better anti-scaling properties of PL-mode #PVDF-CF should be attributed to a higher flow rate and shorter residence time of feed flow parallel to the corrugated patterns, as well as the alleviated concentration polarization. The turbulent effect induced by the perpendicular feed flow on the corrugated patterns and the consequent alleviation of concentration polarization endowed the PD-mode #PVDF-CF with the best scaling resistance.
Results from finite element analyses and laboratory tests are presented which suggest that in the presence of construction induced cracks in new asphalt overlays, geogrid reinforcement will be ineffective in preventing reflective cracking. As is customary, the reinforcement layer was placed at the interface of the overlay and the existing pavement surface. However, when through improved compaction, by means of a newly developed compactor, called AMIR, construction induced cracks were minimized, the same reinforcement proved to be effective in controlling reflective cracking. (A) For the covering abstract see IRRD 857794.
Twelve identical concrete prisms were strengthened with Carbon Fibre-Reinforced Polymer (CFRP) laminate strips on two opposite faces and the laminates were anchored using the newly developed CFRP π-anchor. Prisms were tested in tension to investigate the effectiveness of the anchor to possibly delay delamination and/or to prevent the complete separation of the laminate from the prism. The salient feature of the anchor is its wide head to resist high interfacial shear stresses and its shanks that were inserted in predrilled holes to provide mechanical anchorage and to resist pull-out. The anchor doubled the tensile load-carrying capacity, effectively delayed delamination and prevented the CFRP laminate from full separation. Furthermore, the strengthened prisms experienced noticeable deformation.
To predict the debonding load, shear stresses and strain profile along the FRP-concrete interface for FRP strengthened reinforced concrete members, eleven 4.5m long RC T-beams are built and tested to failure, and their complete load-deflection responses are measured. Three beams are not strengthened and are used as control specimens while the remaining eight beams are strengthened with different amount of CFRP sheet. The same beams are analyzed using LS-DYNA nonlinear dynamic finite element analysis procedure. The predicted load-deflection curve of each beam is compared with its experimental counterpart over its entire loading range up to complete failure, and the two curves are found to be in reasonable agreement. The distinguishing feature of the present analysis is that it not just captures the initiation and propagation of the delamination process, but also the complete post-peak load or softening response of each beam. It is found that the response of FRP strengthened beams is not always brittle and that after the initiation of delamination, the retrofitted beams continue to carry load and undergo appreciable deformation.
