علاء محمد حسن هاشم الحبوبي

Due to the importance of using ambient friendly available materials as an alternative solution instead of the tradition materials in the field of civil construction, present study focuses upon this solution to explore its ability and efficiency when using in the structural members. One of such modern materials is the geopolymer or alkaline concrete which is considered as a green concrete that reduces the evolution of the dioxide carbon during the production process. Also, the recycled components represented by the crushed rubble concrete as course and fine aggregate are also considered here to increase the dependence on the ambient friendly materials that consist the produced geopolymer (green) concrete. In the present study, the geopolymer concrete mix, alkaline concrete with recycled aggregate, is used within the compressive structural elements represented by short hollow steel columns having equal square sections. These columns are tested with and without grouted green concrete as a strengthening material. Usually, the alkaline concrete is produced based on certain molecular ratios that governs the strength of the concrete mix in addition to the role of aggregate ratio. Hence, two values of molecular ratios are adopted in this paper as variable parameters in the concrete mix. Both of the geopolymer concrete mixes are compared with the normal concrete mix as strengthening materials grouted inside the hollow steel columns. Results of axially loaded specimens show that the use of geopolymer (alkaline) concrete with recycled aggregate and different molecular ratios enhances the strength of the steel columns under compressive loads.

The behavior and shear strength characteristics of eight SFRHSC beams strengthened with CFRP strips subjected to combined bending and shear are studied in the present research (in addition to a 9th control beam without CFRP strengthening). The studied variables were shear span to effective depth ratio (a/d) and the deep beam effect, the effect of end anchorage of the CFRP strips with the beams, and effect of the amount of wrapping (width and spacing of the CFRP strips).Tests show that the presence of end anchorage for the strips increases the shear capacity of the beams by 12%for beams with the same properties regardless to the compressive strength.

A new expression for estimating the ultimate eoretical treatmshear strength of steel fibers reinforced high strength concrete (SFRHSC) beams strengthened with CFRP strips based on previous researches is proposed in this research. The proposed expression covers different characteristics and principal parameters such as concrete compressive strength, shear span to effective depth ratio, volume fraction of steel fibers, CFRP amount and distribution, CFRP stiffness, deep beam effect, as well as the end anchorage state of the CFRP strips with the beam. A comparison between computed values and experimentally observed values (with a low COV of about 3.58 %) shows the validation of the proposed thent.

Geopolymer or alkaline concrete is a modern binder material characterized as an ambient friendly product within the construction field. Present study has investigated the geopolymer concrete mix used in the dome structural members compared with the use of ordinary concrete mix. Geopolymer concrete mixes are produced according to certain molecular ratios govern its design strength, so that present study has adopted molecular ratio of 14 mole (14M) as an alkaline molar concentration forming a binder material for the coarse and fine aggregate. Laboratory tested coarse and fine aggregate were used in both of geopolymer and ordinary concrete mixes. Two models of domes were made using geopolymer concrete mix while other two models were casted by the ordinary concrete mix and both types were reinforced with single layer of steel wire mesh. Later, all models were tested under uniaxial concentrated load subjected vertically on the peak of dome. Results showed that high ultimate failure load could be achieved for the geopolymer reinforced concrete as well as in the ordinary reinforced concrete when they subjected to a concentrated load on the dome's peak.

This paper presents the behavior of the helical reinforced concrete columns (HCC) subjected to horizontal 2D seismic motion excitation combined with the static axial load. Helical concrete columns are new types of elements which arose in the new twisted buildings, providing a special geometry by twisting the top section by an angle (ϕ), furthermore, offsetting the top section by a considerable distance respecting to the bottom section. In order to study seismic behavior of the HCC under a seismic load of the short period using finite element software, numerical simulation is carried out in this paper using ANSYS V 18.1 software. A brief comparison of the HCC behavior was made between different cases of conventional reinforcement in the longitudinal and transverse directions, as well as the different twisting angles (ϕ) of column sections. The comparison illustrated that all columns response with giving the same mode shapes of vibration in the modal analysis with different values of natural frequencies and relative amplitude deformations. However, the difference be very noticeable when changing the section size of the columns comparably with changing the twisting angles of the section, where increasing the section size of HCC from 250 mm to 400 mm cause increase the natural frequency by 55.4% for second mode shape, while it cause decreasing the relative amplitude response of HCC by 52.5% for sixth mode shape. The transient analysis of the six types of HCC excited by horizontal 2D seismic motion indicates the tendency of HCC to increase its responses, like twisting and buckling deformations. The deform shape-time history of 6 HCC demonstrated that with increasing (shear stress path section distance) S of HCC column which depends up on (ϕ value), the top section would have less stresses.

This study proposes replacing the ordinary reinforcing bars of the one-way concrete slab by embedded steel plate cutting using CNC method. The new proposed structural model is analysed under blast loading. This type of model is very important in special structures such as a military warehouse to increase withstanding of the structural slab when the explosion has occurred. Two concrete slab models were numerically tested, the first is with ordinary reinforcement and the other is with embedded CNC steel plate only. The ordinary RC slab model was adopted from literature to verify the procedure of analysis under blast loading in this research. A parametric study on this first model was implemented to investigate the effect of changing in material properties, blast load properties, reinforcement steel ratios and stiffness on the behaviour of dynamic response for the slab model. The second proposed model was simulated using embedded CNC steel plate with keeping an equivalent moment of inertia and area of ordinary reinforcement in the cross section of the slab. Also, two types of the opening shapes in the CNC plate, square and circular, and two sizes of openings, 37.4 mm and 155.7 mm, were investigated. The finite element analysis of the model was implemented using ABAQUS Explicit-software. The blast load was generated using the CONWEB model provided in ABAQUS software. The results extracted from the analysis of the proposed model are compared with those extracted from the original model. The maximum displacement in the mid-span of the slab is the reference parameter to perform the comparison. The results exhibit significant effect of the proposed model by reducing the maximum displacement in the slab model by reduction percentage of 12.1%.