الفهرس 
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Abstract
The main aim of this study is to investigate the effectiveness of applying CFRP as a strengthening technique to the CWSBs in improving the shear capacity. In this study, experimental investigation is conducted on five CWSBs, with one control un-strengthened specimen and four strengthened specimens. The study takes into consideration different CFRP strips schemes and arrangement over the entire web in the shear zone of CWSBs. A numerical analysis is conducted using a finite element (FE) model developed in ANSYS software. The proposed FE model results are validated against the experimental ones. Using the validated FE model to analyze, parametric studies are conducted involving 75 CWSBs to investigate the influence of different parameters, including web slenderness ratio, fold slenderness ratio, fold aspect ratio, CFRP strip length to web height ratio, CFRP strips thickness, CFRP schemes and CFRP arrangement over the entire web.
7.2. Conclusions
The results have demonstrated the efficiency of using CFRP strengthening technique in enhancement the shear capacity of CWSBs up to 68.61% depending on CFRP configuration. The parametric studies have revealed that there are effective parameters which control the efficiency of CFRP strengthening technique.
The following observations are made based on the limited scope of this study.
1- Applying CFRP strip on steel web of CWSB is an effective strengthening method in enhancing the shear capacity of CWSB, in which the contribution of the CFRP strips, attached to the web, let the beam gain more capacity than un-strengthened beam, and postpone web buckling.
2- The increase in the shear capacity of CWSBs strongly depends on CFRP configuration, as from the findings, it is highly recommended to apply CFRP strips on horizontal and inclined folds on both-fold sides (RMB) which proves to be the best CFRP configuration among all, as it achieves the maximum gain in shear capacity increasing by 68.61 %. Whereas, a minimum gain in shear capacity increasing 24.7 % is achieved by applying CFRP strips on horizontal fold only on one-fold side (RHO).
3- CFRP strengthening for CWSBs achieves a significant decreasing in both strain on steel web and CFRP strain.
4- CFRP debonding in all strengthened beams occurs at the ultimate load capacity, whereas four failure modes are observed during the test depending on the type of CFRP configuration. These modes are steel/adhesive interface debonding, CFRP/adhesive interface debonding, CFRP delamination and CFRP splitting.
5- Also, the failure modes in beam depends on the type of CFRP configuration, as, interactive web buckling is observed for beam strengthened by applying CFRP on horizontal folds only, whereas for beam strengthened by applying CFRP on horizontal and inclined folds, the observed global web buckling is the same as control beam.
6- The FE simulation results are consistent with the test results and accurately reflects the real overall behaviour of the CWSBs.
7- The effects of different parameters on strength have been presented using bar charts which clearly reveal the sensitive parameters that have the major effect on strengthening efficiency, as follow:
The effect of CFRP strengthening on thick web is higher than that of thinner ones.
The increase in the length of the CFRP does not result in a significant benefit in beam capacity increasing, as the CFRP strip length / web height which is 70% has already covered the part exposed to the maximum tensile stress in the web, and any other increase will not help much.
The strength gains increases with the increase in CFRP thickness which can significantly prevents or delays the onset of local buckling.
The CFRP strengthening has the greatest effect on the beams with a local buckling mode corrugation (L), compared to the beams with a global buckling corrugation (G).
Among all CFRP configurations, applying CFRP on horizontal and inclined folds on both-fold sides has the largest strength gain increasing.
8- A proposed design procedure for predicting the design shear buckling strength of CWSBs strengthened by CFRP is presented. The results of the comparison of the proposed model prediction and FE results show a good consistency, which indicates the accuracy of the proposed formula.
7.3 Recommendations for future work
Future research can be directed in several areas in CFRP strengthening technique and gain a more detailed understanding of the bond behaviour. This can be as follows:
1- Research on the fatigue and environmental effects on the long-term durability and performance of the steel/CFRP bond interface should be carried out.
2- Studies is needed in the CFRP strengthening effects on strength in case of using high -modulus CFRP, ultra -high -modulus CFRP and high modulus adhesive layer.
3- It will be beneficial to conduct an experimental shear strength test for the adhesive epoxy to validate the behaviour of the epoxy in shear.
4- Experimental work is necessary to study the effects of tapering the CFRP strip edges in order to reduce the bond stresses at the end of the strip.
5- Further study on the use of CFRP strips to delay the onset of buckling may be beneficial, not only for beams but also for thin-walled structured with any sections.
6- More studies are recommended to conduct large number of laboratory tests and FE simulation in a various dimension of strengthened CWSBs to obtain an accurate design model for strengthened CWSBs in different ranges.