Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Shear Strength

Effect of Shear Span-Depth Ratio on Shear Strength of Porcelanite Lightweight Aggregate Reinforced Concrete Deep Beams Strengthened by Externally Bonded CFRP Strips

K.F. Sarsam; N.A.M. Al-Bayati; A.S. Mohammed

Engineering and Technology Journal, 2017, Volume 35, Issue 3, Pages 267-275

This paper presents an experimental investigation of structural behaviour of reinforced concrete deep beams strengthened in shear by CFRP strips. The experimental program consisted of fabricating, casting and testing of nine identical porcelainte lightweight aggregate reinforced concrete deep beams. Three of the tested deep beams were unstrenghtened to serve as reference beams, while the remaining beams were tested after being strengthened using CFRP strips in two different orientations (vertical and horizontal). The locally available natural porcelanite aggregate is used to produce lightweight aggregate concrete. The beams were designed to satisfy the requirements of ACI 318M- 14 building code. In order to insure shear failure modes, adequate flexural steel reinforcement were provided. Effect of three different values of shear span to effective depth ratio (a/d =1.0, 0.8, 1.2) were selected. All beams have been tested as a simply supported beams subjected to two concentrated points loading. The beam specimens were tested up to failure under monotonic loads. The experimental work showed that the failure load increases as the shear span to effective depth ratio deceases. As the shear span to effective depth ratio decreased from 1.0 to 0.8, the percentage of increase in the ultimate load was about 24%. In addition, the diagonal compression strut crack of unstrenghtened control beams was changed to several diagonal cracks at mid depth within the shear span of the strengthened beams and exhibited more ductile failure mode.

An Experimental Study on the Shear Strength of High-performance Reinforced Concrete Deep Beams without Stirrups

Sinan Abdulhkaleq Yaseen

Engineering and Technology Journal, 2016, Volume 34, Issue 11, Pages 2123-2139

High-performance fiber-reinforced concrete is a new class of concrete that has been developed in recent decades. It exhibits enhanced properties such as high compressive strength and improved tensile strength. Three types of concrete with different compressive strengths, namely, normal-strength concrete, high-strength concrete, and high-performance concrete, were used in this study. The experimental program included casting and testing sixteen reinforced concrete deep beams without stirrups to study the shear strength and behavior of these beams under two-point loading. The variables considered were the compressive strength of concrete (f′c ) (40–120 MPa), shear span-to-depth ratio (1, 1.5, 2, 2.5, and 3), and the ratio of the amount of flexural steel bar ratio (1.35%, 2.40%, 3.76%, and 6.108%). Experimental results showed that increasing concrete compressive strength and flexural steel bar ratio increased ultimate shear capacity. By contrast, increasing shear span-to-depth ratio and span-to-depth ratio reduced ultimate shear capacity. Based on the test results of this investigation (16 beams) and those of available literature (233 deep beams), an equation that considered the parameters affecting shear stress (f′c, l/d, a/d, andw) was proposed using SPSS software. The proposed equation was compared with predictions made by the American Concrete Institute (ACI) and the works of other researchers, including that of Zsutty and Aziz. The ACI predictions were conservative and the proposed equation had a lower coefficient of variation.

Experimental Study on Compressibility, Volume Changes, Strength and Permeability Characteristics of Unsaturated Bentonite-Sand Mixtures

Mohammed Y. Fattah; Nahla M. Salim; Entesar J. Irshayyid

Engineering and Technology Journal, 2016, Volume 34, Issue 7, Pages 1308-1323

Expansive soils are generally found in arid and semiarid regions. These soils undergo volumetric changes upon wetting and drying, thereby causing ground heave and settlement problems. This characteristic causes considerable construction defects if not adequately taken care of. Solving the unsaturated soil problems needs the assessment of suction variation in time and space as a response to the variation of environmental factors such as rainfall and evaporation.
To investigate the effect of the changes of the soil suction on the volume changes, expansion index, swelling pressure, shear strength and the coefficient of permeability, small scale experiments were conducted using pure bentonite and the bentonite mixed with sand in proportion of: 30%, 40% and 50% at different initial water contents and dry unit weights was chosen from the compaction curves. The study shows that the swelling-potential, swelling-pressure, the soil-suction, the soil-strength and the coefficient of permeability are affected by the initial-conditions (water-content and dry-unit weight), where all these parameters except the permeability-coefficient marginally decrease with the increase in soil-water content, while the coefficient-of permeability increases with increasing the water-content.