A new adhesive beam-column connection is tested which possess the highest strength and stiffness compared to any other similar adhesive or bolted connection tested in the past. A square GFRP hollow section, acting as a column, was connected to a built-up beam made of two GFRP U-profiles by means of either epoxy or steel bolts. The beam-column assembly formed an L-shaped frame which was tested by applying a point load at the beam free end while the column was fixed at its base. Five bolted and five adhesive replicate connections were subjected to quasi-static loading up to failure. Another three adhesive connections were subjected to 400, 800 or 1200 cycles of loading and unloading with the maximum load being equal to 0.50 Pu,avg, where Pu,avg is the average static strength of the replicate adhesive specimens. At the end of the cyclic loading, the latter specimens were loaded quasi-statically to failure. Finally, another two adhesive connections were subjected to fatigue type loading. They were successively subjected to at least 196 cycles of loading and unloading with the load amplitude being 0.50 Pu,avg in the first 60 cycles, 0.75 Pu,avg in the next 60 cycles, 0.85 Pu,avg in the following 60 cycles and 0.95 Pu,avg after the 180th cycle. The test results show that the proposed adhesive connection can achieve on average 82% higher strength and 380% higher rotational stiffness than the companion bolted connection. Furthermore, the above cyclic loading has negligible effect on either the strength or the stiffness of the connection. Finally, the connection can sustain the foregoing fatigue load up to almost 180 cycles without significant damage but it will not be able to withstand the full 60 cycles of the load with 0.95 Pu,avg amplitude. The current results demonstrate the superior strength and stiffness of the new adhesive connection compared to a similar bolted connection.
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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.
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.
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.
The fiber-reinforced polymers (FRP) bar is a promising solution to problems caused by steel rebar corrosion in concrete. To assess the service life of the FRP bar based on accelerated test results, it is crucial to have a reliable model. Here, a modified exponential (MEP) model is proposed based on the Avrami equation. The Avrami equation provides a theoretical foundation for the empirical exponential (EP) model and does not a priori fix the power of the exposure time to one. A database containing 903 data points from 74 groups of test specimens is assembled to compare the reliability of the MEP model vis-a-vis the EP, single logarithmic, double logarithmic, and power function models. The combination of Root Mean Square Error (RMSE), the Mean Absolute Error (MAE), and the coefficient of determination (R2) criteria is proposed for assessing model reliability. It is shown that in certain cases the combined criteria, versus R2 alone, significantly increase the number of test groups meeting the acceptable performance limit. Observed test data aberrations are found to have minor influence on the results of the EP model, but they significantly influence the results of the other four models. The EP model generally predicts the lowest activation energy and the smallest strength retention for similar groups of bars, while the predicted values of the other four models exhibit a relatively small difference. The difference between the predicted strength retention values of the EP and MEP models shows an increasing trend with the increase of the absolute value of (1 − n), where n is the power of the exposure time in the MEP model.
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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.
PCM Trombe walls have been an effective passive technology to achieve energy efficiency. However, the majority of previous research investigated the PCM Trombe walls primarily focused on structural improvement, and very few studies have focused on mixed-dry climate Therefore, in this study, ten scenarios were created and simulated by the validated CFD model under a mixed dry climate. The findings indicate that in summer, an external PCM layer with a melting point of 38 °C could reduce the maximum peak load by 48.9 %, decrease the fluctuation amplitude by 76 %, reduce the cooling load by 14.4 %, compared to the reference case, and yields time lags of 4.5 h and 6.1 h for the maximum and minimum indoor temperatures, respectively. In winter, an external PCM layer with a melting point of 30 °C can reduce the thermal load by 38.2 %, decrease the fluctuation amplitude by 28.5 %, compared to the reference case, and achieve time lags of 4.0 h and 1.7 h for the minimal and maximum indoor temperatures, respectively. Overall, the PCM layer should be placed adjacent to the air channel, and the appropriate PCM melting points in summer and winter are different.
Shrinkage cracking is one of the factors that cause deterioration of reinforced concrete structures. The cracks facilitate the ingress of moisture, oxygen and chlorides to the steel reinforcement surface, which results in steel corrosion and subsequent deterioration of the structure. In this paper, a field investigation was conducted and a monitoring program was designed and implemented to evaluate the performance of the polymer grid in controlling shrinkage cracking under realistic conditions. The monitoring program extended for a period of three years. At the end of the three years period, some samples were cored from the cracked sections and transferred to the laboratory to measure the variation of crack width through the depth and the residual tensile strength of the partially cracked cores. The results show that the polymer grid reduced both the width and density of shrinkage cracks, and endowed partially cracked concrete with higher residual tensile strength. Also, limited and preliminary data indicate that the grid reduced the permeation of chlorides from deicing salt.
The flanges of T- and I-beams are subjected, near their junctions with the web, to three in-plane forces: N x , N y , and N xy , where x and y are horizontal axes parallel and normal to the beam axis. The finite element method is used to study the variation of these forces in T-beams under point or line load. It is concluded that forces N x and N xy can be determined for design purposes using conventional engineering beam theory. Force N y , on the other hand, cannot be determined by available closed-form solutions. Based on a detailed parametric study, a simplified procedure is proposed for determining N y . Key words: beams (supports), connections, finite element, flanges, loads (forces), T-beams, webs (supports).
