This paper investigates ultimate strength of lightweight concrete specimens: cubes, cylinders, and prisms wrapped by different layers CFRP respect to several curing periods. The specimens were prepared and tested under compressive and flexural loading at the ages of 7 days and 28 days with varying confinement levels (from unconfined; 0L to double-layer of CFRP, i.e., 2L). The results showed that all three factors: confinement level, specimen geometry and curing age had a significant effect on both compressive strength as well as flexural strength. Indigenous soft soil was wrapped with various CFRP wraps to study the change in failure mode from brittle to ductile with an increase in confinement and two-layer WR-CFRPs exhibited the maximum gains in compressive and flexure-up to 48% compressive, 380% of flexural strength when compared with unconfined specimens. Cylindrical samples prove always more pronounced strengthening effect than cubes, probably because of having a more even stress field and less influence to the corner effects. Besides, the confinement effect became more significant when specimens were left to cure for 28 days, highlighting initiation of concrete maturity requirement for best CFRP development. The findings indicated that early-age confinement (7-day, 2L) achieved strength equal or superior to shear-critical fully cured unconfined specimens, and confirmed the potential of CFRP in emergency repair and retrofitting. However, the ultimate strengths were the best when using both multi-layer CFRP confinement and full curing. These results highlight the synergistic relationship between geometry optimization, curing regimen and advanced fiber reinforcements in enhancing the structural response of lightweight concrete structure.
This paper presents a nonlinear finite element analysis of reinforced concrete beams subjected to pure torsion. A verification procedure was performed on three specimens by finite element analysis using ANSYS software. The verification with the experimental work revealed a good agreement through the torque-rotation relationship, ultimate torque, rotation, and crack pattern. The studied parameters of strengthening by CFRP sheets included strengthening configurations and number of CFRP layers. The confinement configuration methods included full wrapping sheet around the beam, U-shaped sheet, ring strips spaced at either 65 or 130 mm, longitudinal strips at the top and bottom faces, U-shaped strips in addition to the number of layers variable. It was found that the performance of the beam for resisting a torsional force was improved by (33-49%) depending on the method of coating with CFRP sheets and the number of used layers. A change in the angle of twist, as well as the shape of the spread of cracks, was also noticed from the predicted results.
The main purpose of this search is to study the punching shear behavior of fourteen specimens of Reactive Powder Concrete (RPC) two-way flat plate slabs, half of these slabs have been exposed to a high temperature up to 400 C° by using an electric oven. All slabs have dimensions of (400x400x60) mm, with steel reinforcement mesh of (Ø6mm) diameter. Laboratory tests show that there is an increase in the value of First Crack Loading (FCL) and Ultimate Load (UL) by (208, and 216.67) % and a decrease in deflection by (56.85) % due using slab with complete reactive powder relative to a slap made of normal concrete. The use of the (RPC)mixture in layers in slabs gave results close to the slab which consists of full (RPC) this gives the benefit of more than the use of a slab that contains full reactive powder concrete in terms of cost, the increase was in FCL and UL by (130.8, 169.23, 102.7 and 135.135) % and a decrease in the value of deflection by (37.17, 47.64) %. The use of a partial reactive powder mixture also showed good results, and by increasing the dimensions of the RPC area, the results were better. the increase in FCL and UL by (54, 116, and 185) % and (53, 116.67, and 166.67) % and a decrease in value of deflection by (36.12, 42.4, and 50.26) % from reference slab. When slabs are subjected to high temperatures, there may be a decrease in the value of the FCL and UL and an increase in the value of deflection when compared to models not exposed to high temperature. But when compared to the reference slab with the same circumstance showed an increase in the value of the FCL and the rate ranged between (50- 200) % and the UL was the ratio ranged between (51.35-208.1) % and a decrease in the value of the deflection where the ratio ranged (21-46) %
The behaviour of high-strength fiber reinforced concrete columns was observed with a testing program of 7 columns, loaded eccentrically. The theory was analyzed by modifying the stress block diagram of concrete. The experimental results show that using high-strength fiber reinforced concrete with fiber volume fraction of 1.0%, increased the column ultimate capacity up to 40% in addition to increasing its ductility and toughness, significantly. The proposed theoretical analysis gave a good estimation of experimental results.