حيدر احمد عبد الكاتب

Reinforcing the wooden structural members is considered as a challenging matter to overcome the drawbacks of using wood in the construction field. The current investigation, therefore, presents an attempt to evaluate the effectiveness of utilizing steel bars as reinforcements in glulam timber beams using the near-surface-mounted (NSM) technique in conjunction with carbon fiber-reinforced polymer (CFRP) sheet wraps. A series of flexural testing was carried out until failure for both reinforced and unreinforced glulam members in a simple support system. Eleven specimens were examined in two groups to compare them with the control beam. Five reinforced glulam (RG) beams of the first group were reinforced with different schemes at tension and compression zones using the same bar size. The other five specimens of the second group were reinforced with shear reinforcement using fully wrapped strips made of CFRP sheet in addition to the same flexural reinforcement schemes as the first group. Each glulam beam has a span of 1.35m and a rectangular section sized 85mm × 175mm. Based on experimental outcomes, theoretic modeling was provided to estimate the ultimate load capacity and bending rigidity of reinforcing glulam members. Though several theoretical predictions of flexural capacity were overstated when compared to experimental predictions, these disparities were frequently about 10%, confirming that the proposed theoretical model was accurate, and the mean of ultimate loading capacity and deflection between experimental and theoretical results were 1.01 and 1.09, respectively. Experimental results presented show that the RG beams performed much better than the unreinforced reference beams in terms of structural behavior, with improvements in ultimate load capacity ranging from 16 to 49%. On the other hand, the shear reinforcement for RG members slightly improved flexural performance, and the ultimate load capacity increased by 2–7%. Therefore, it was concluded that the NSM techniques using ordinary steel bars were effective ways in strengthening the glulam members in terms of flexural stiffness with increasing ultimate load capacity

Due to the important roleThe current study included an experimental examination of the structural behavior of standard wooden beams strengthened in flexure using carbon fiber reinforced polymer (CFRP) sheet, and aimed at determining the effective length and width of the strengthening CFRP sheet. The study included testing of ten standard timber beams using four-point loading method. One of the standard timber beams was non-strengthened and the others were strengthened with CFRP sheets. The strengthened timber beams were divided into three groups depending on the width of the strengthening CFRP sheet. Each group contains three specimens with different lengths for the strengthening CFRP sheet. Experimental results showed that there is a range for the effective length of the strengthening CFRP sheet. Moreover, the research also find out that the increase in sheet width (CFRP area ratio) does not always lead to a consistent improvement in the flexural behavior of the timber beams. Finally, it can be concluded that the CFRP sheet could be more effective in strengthening the timber beam in flexural when the sheet length extends beyond the region of maximum bending moment but not further than the sections with moments lower than half the maximum moment and its width equal to beam width.

This paper presents a study of the shear action of T-shaped reinforced concrete hybrid beams with a circular hole in various horizontal positions. All beams were tested as simply supported beams with two-point loads. Seven specimens were evaluated, all of which were similar, the section had two concrete strength layers, it was designed according to (ACI 318-2019), the first specimen being a control beam with no hole or CFRP strengthening. Every two specimens have the same circle size and location within the shear zone; however, one lacks CFRP strengthening. The opening affected the beam stiffness in the elastic stage, serviceability stage, plastic hinge stage, and ultimate shear failure. The ultimate failure load for the beams with an opening (located at the distance from the center of the circle hole to the support) at 150mm,350mm, and 550mm were (-31.03 %, -34.48 %, +10.34% respectively, compared with that in the control beam. however, the use of CFRP strips in the beams compared with the other beams, that have a similar location of circular holes increased the strength to 20.69%, 44.83%, and 31.03%, respectively. As a result, this result provided a good opportunity to obtain a suitable hole placement, and a good way to strengthen the CFRP strips. Keywords: Shear, isolated, hybrid, T-beam, opening, CFRP strips

Slab–Column connection is one of the critical structural joints in building construction, since there are special design requirements that must be achieved. This paper investigates RC slab–column connections under eccentric load using a built-in 3-Dimensional Nonlinear program of finite element in the pre- and post-cracking levels and up to the ultimate load. The concrete is simulated as isoparametric brick element, and the reinforcement bar elements are assumed to be built into isoparametric brick elements. With regard to load–deflection responses and ultimate strength capacity, a good coincidence is achieved for FEA and experimental results with maximum difference 1.6% for ultimate strength. In addition, the structural performance investigation of slab–column connection is carried in terms of the effectiveness of applied load types, shear reinforcement and slab thickness. It can be concluded that the increase in loading eccentricity cause decreasing in ultimate load 20.5 to 40% in comparison with case of e = 0, which is one of conclusion of this research. Also, the use of shear reinforcement (48 stirrups of Φ10 mm) in the flat slab connection with columns had more effects than slab depth. It is found that the ultimate load capacity increases about 34.4% with e = 0.0, while it decreases about 22% with e = 0.45 m when compared with slab–column connections without shear reinforcement (e = 0.0). In addition, as the slab thickness increases from 150 to 200 mm, the ultimate load increases about (25%) when compared with case of (e = 0.0), while the ultimate load increases about (2.3%) when compared with the same case of (e = 0.0), which means that the increment in the slab thickness can be considered as compensation for the effects of increasing in load eccentricity. Also, for the slab–column connection without shear reinforcement, the related formula of ACI-code gives a good agreement in terms of ultimate load capacity in comparison with the results of adopted FE model with maximum difference 4% as the unbalanced moment was increased, while for usage of shear reinforcement in slab–column connection, the formula of ACI-code becomes more conservative with maximum difference 10% with increasing of unbalanced moment.

Due to the important role of high strength concrete in the structural systems, present work focuses on the use of this material as a strengthening technique incorporating with the normal strength concrete in fl at slab system. Eight simply supported fl at slab models with (1,000 × 1,000 × 120 mm) dimensions are investigated based on three groups including normal strength concrete and high strength concrete. The fi rst group represents models containing of two fl at slabs fully with one type of concrete; NSC and HSC as control fl at slab. The second and third groups consist of six fl at slabs as hybrid fl at slabs of two layer of concrete with different thicknesses. Concrete mixture HSC was used in tension zone in three hybrid fl at slabs (second group) with three thicknesses (30, 60 and 90 mm), while the remaining three hybrid fl at slabs (third group) was used the HSC in compression zone with the same previous thicknesses. The experimental results shown that the ultimate load increased about (19.4%) when HSC was used fully (hH / h = 1) instead of using NSC in the control fl at slab (NSC slab). The hybrid fl at slabs with use HSC in compression zone showed higher in cracking and ultimate fl exural loads compared with those of the hybrid fl at slabs with use HSC in tension zone and also were stiffer in load-defl ection curve with the hybrid fl at slabs with HSC in tension zone, also the hybrid fl at slabs showed an improvement in the cracking load and ultimate fl exural load when increasing the thickness of the HSC layer (hH / h) in both tension and compression zone as compared to control fl at slab (NSC slab).

Fiber reinforced concrete is an improved type of concrete that containing fibers randomly distributed inside it. Usually, the mechanical properties of concrete have been developed namely, compressive, flexural, and tensile strength by adding the fibers. In addition, the fiber makes the concrete very durable, tougher and lower permeability. This paper aims to enhance the concrete mechanical properties by adding polypropylene fibers in combination with high performance cement as a partial cement replacement. The combination of both polypropylene fibers and high performance cement in concrete gave excellent values of flexural, tensile and compressive strength. Seven percentages of polypropylene fibers were used while two percentages of high performance cement were used, in addition to normal specimens of concrete without any admixtures. Test results give a well improvement by using both polypropylene fibers and high performance cement. The flexural strength and the tensile strength are increased significantly from 2.7 to 14.5 MPa, and from 1.9 to 7 MPa, respectively. While concrete strength of compression increased from 30.1 MPa to 42.9 MPa due to inclusion of polypropylene fibers and high performance cement. The concrete specimens with including both high performance cement and polypropylene fibers had adequate strength to counteract further cycles of loading after releasing 1st failure load.