Investigations on the influence of radial confinement in the impact response of concrete

Yousef Al-Salloum,Saleh Alsayed,Tarek Almusallam,S.M. Ibrahim,H. Abbas 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.14 No.6

Annular and solid concrete specimens with different aspect ratios and static unconfined compressive strengths were studied for impact loading using SHPB test setup. Numerical simulations in LSDYNA were also carried out and results were validated. The stress-strain curves obtained under dynamic loading were also compared with static compressive tests. The mode of failure of concrete specimen was a typical ductile failure at high strain rates. In general, the dynamic increase factor (DIF) of thin solid specimens was higher than thick samples. In the numerical study, the variation of axial, hydrostatic and radial stresses for solid and annular samples was studied. The core phenomenon due to confinement was observed for solid samples wherein the applied loads were primarily borne by the innermost concrete zone rather than the outer peripheral zone. In the annular samples, especially with large diameter inside hole, the distribution of stresses was relatively uniform along the radial distance. Qualitatively, only a small change in the distribution of stresses for annular samples with different internal diameters studied was observed.

Prediction of compressive strength of concrete using neural networks

Yousef A. Al-Salloum,Abid A. Shah,Saleh H. Alsayed,Tarek H. Almusallam,M.S. Al-Haddad,H. Abbas 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.10 No.2

This research deals with the prediction of compressive strength of normal and high strength concrete using neural networks. The compressive strength was modeled as a function of eight variables: quantities of cement, fine aggregate, coarse aggregate, micro-silica, water and super-plasticizer, maximum size of coarse aggregate, fineness modulus of fine aggregate. Two networks, one using raw variables and another using grouped dimensionless variables were constructed, trained and tested using available experimental data, covering a large range of concrete compressive strengths. The neural network models were compared with regression models. The neural networks based model gave high prediction accuracy and the results demonstrated that the use of neural networks in assessing compressive strength of concrete is both practical and beneficial. The performance of model using the grouped dimensionless variables is better than the prediction using raw variables.

Post-Heating Response of Concrete-Filled Circular Steel Columns

Husain Abbas,Yousef Al-Salloum,Saleh Alsayed,Mohammed Alhaddad,Rizwan Iqbal 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4

Concrete-Filled Steel Tubular (CFST) columns are increasingly becoming popular for carrying heavy loads. One of the major concerns for such columns has always been the exposure to fire and subsequent cooling for which different methods are adopted. This study investigates the effect of cooling regimes after exposure to elevated temperature of 600oC for three hours on axial compression behavior of concrete-filled circular stub columns. The experimental program involves the testing of thirty columns consisting of two sizes of outer steel tube. Double skin columns were also considered for the bigger diameter column. The cooling regimes considered in the study were annealing and water quenching. The columns were tested for two possible modes of load transfer viz. core loaded and composite loaded. The behavior of columns was studied in terms of ultimate load capacity, loaddeformation pattern and stresses in the materials. The ductility of concrete-filled columns was higher than that of the steel tube alone. The confinement offered by outer steel tube was less in composite loaded columns as compared to core loaded columns. The annealing was found to be slightly better than water quenching for post-fire cooling of columns.

Behavior of FRP‑Strengthened RC Beams with Large Rectangular Web Openings in Flexure Zones

Tarek Almusallam,Yousef Al?Salloum,Hussein Elsanadedy,Abdulhafiz Alshenawy,Rizwan Iqbal 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.5

This paper aims to investigate the behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams containing large rectangular web openings in the flexure zone. Studied parameters were type of loading, opening size and strengthening scheme. Seven RC beams categorized into two different groups were tested. In the first group, two unstrengthened beams (one solid without opening and one with large rectangular web opening in the pure flexure zone) were tested under four-point bending. In the second group, five beams were tested under center-point loading. They comprised of one reference solid beam and four beams with large rectangular web opening in the maximum-moment region. Out of the four beams with openings, two specimens were unstrengthened and the other two were strengthened with two different FRP schemes. A numerical study was also conducted and the results of analysis were validated with experiments. The calibrated analysis was then used for some useful parametric studies in which the effect of different parameters was investigated.

Prediction of Punching Shear Strength of HSC Interior Slab-Column Connections

Hussein M. Elsanadedy,Yousef A. Al-Salloum,Saleh H. Alsayed 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.2

Flat plate systems are widely used in reinforced concrete structures. Using of high-strength concrete has been common recently. In the current international codes of practice for concrete structures, the design methods for assessment of punching shear capacity are based on experimental data of flat plates with Normal-Strength Concrete (NSC). The aim of this research is to come up with new formula for punching shear resistance, consistent with data of flat plates made from High-Strength Concrete (HSC). Test results of 61HSC interior slab-column connection specimens were collected from the literature. The available test results were not only compared with current code provisions but with equations proposed by other researchers as well. A new formula for predicting punching shear strength of HSC interior slab-column connections is proposed. An innovative design equation is also suggested.

Reliability Assessment of HFRC Slabs Against Projectile Impact

Nadeem A. Siddiqui,Yousef A. Al?Salloum,Tarek H. Almusallam,Aref A. Abadel,Husain Abbas 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.6

In the present study, a probabilistic procedure is presented for estimating the reliability of hybrid fiber reinforced concrete (HFRC) slabs against the impact of hemispherical nose projectiles considering uncertainties involved in the material, geometric and impact parameters. The influence of hybrid fibers in improving the safety level of reinforced concrete slabs against impact loads has also been studied on a parametric basis. The failure of the HFRC slabs was assumed to occur when the impact velocity of the projectile exceeds the ballistic limit of the slab i.e. perforates the slab. To illustrate the procedure, a probabilistic analysis was carried out on the impact test results of HFRC slabs containing different proportions of hooked-end steel, polypropylene and Kevlar fibers, recently published by the authors. Reliability assessment was performed for a range of applied nominal impact loads by varying the impact velocity of the given projectile. Reliability analysis yields the safety level of all the HFRC slabs against the impact of the above projectile. Effect of fibers, especially steel fibers, and slab thickness on the reliability of HFRC slabs are also investigated on a parametric basis.

Mechanical Properties, Phase Composition and Microstructure of Activated Metakaolin-slaked Lime Binder

M. S. Morsy,Y.A. Al-Salloum,T.H. Almusallam,H. Abbas 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.3

In the present paper mechanical properties, microstructure and phase composition of binder produced by mixing Metakaolin (MK) and slaked lime in 4:1 proportion by weight have been studied. Anhydrous Gypsum was mixed as an activator in different percentages of 0%, 5%, 10%, 15% and 20% by weight of the binder. The study measures the changes in the physical properties, flexural and compressive strengths of the mortar at different ages of curing varying from 2 to 28 days. Binder and sand were mixed in 1:1.5 proportion for the mortar preparation. Superplasticizer Glenium 51 was added by 1% weight of the binder. The curing of demolded mortar specimens were done at room temperature for 2 to 28 days. The optimal dosage of anhydrous gypsum was found as 5% by weight of the binder at which bulk density, compressive and flexural strengths of mortar were maximum and the total porosity and water absorption were minimum. Addition of 5% anhydrous gypsum increases the compressive and flexural strengths by 68.5% and 72.1% respectively. The composition and microstructure of the mortar confirm the trend of variation of mechanical properties of the mortar

Experimental and FE Study on RC One-Way Slabs Upgraded with FRP Composites

Hussein M. Elsanadedy,Tarek H. Almusallam,Saleh H. Alsayed,Yousef A. Al-Salloum 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.4

The use of externally bonded Fiber Reinforced Polymer (FRP) composites as a means of upgrading the flexural capacity of Reinforced Concrete (RC) one-way slabs is experimentally and numerically investigated in this study. A total of four groups of eight slabs were tested under four-point bending. The two slabs of the first group were left unstrengthened to be used as control specimens. The two slabs of the second group were externally strengthened with adhesively bonded pultruded, pre-cured CFRP plates. The four slabs of the last two groups were externally upgraded with unidirectional carbon (or E-glass) fiber fabric impregnated with an epoxy resin. In addition to the experimental program, a numerical investigation utilizing nonlinear Finite Element (FE) analysis was conducted using LS-DYNA software. Besides the eight slabs tested in this study, another eleven slabs were collected from the literature for the purpose of finite element validation. A comparison was made between the experimental and numerical results and good agreement was achieved. Based on FE validation, the numerical analysis was extended to include additional cases to study the effect of axial FRP stiffness and FRP-to-concrete width ratio on the flexural performance of upgraded slabs. As a result of the numerical study, new stiffness and reinforcement parameters were introduced in this research. These parameters were employed in the development of two new formulas for predicting the FRP debonding strain and percent gain in flexural capacity of FRPstrengthened slabs.

Progressive collapse analysis of a RC building subjected to blast loads

Almusallam, T.H.,Elsanadedy, H.M.,Abbas, H.,Alsayed, S.H.,Al-Salloum, Y.A. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.3

The paper seeks to explore some aspects of the current state of knowledge on progressive collapse in the technical literature covering blast loads and structural analysis procedure applicable to reinforced concrete (RC) buildings. The paper describes the progressive collapse analysis of a commercial RC building located in the city of Riyadh and subjected to different blast scenarios. A 3-D finite element model of the structure was created using LS-DYNA, which uses explicit time integration algorithms for solution. Blast loads were treated as dynamic pressure-time history curves applied to the exterior elements. The inherent shortcomings of notional member removal have been taken care of in the present paper by simulating the damage of structural elements through the use of solid elements with the provision of element erosion. Effects of erosion and cratering are studied for different scenarios of the blast.

Experimental Investigation on Vulnerability of Precast RC Beam-column Joints to Progressive Collapse

Tarek H. Almusallam,Hussein M. Elsanadedy,Yousef A. Al-Salloum,Nadeem A. Siddiqui,Rizwan A. Iqbal 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

The multi-story buildings are susceptible to progressive collapse in the event of the removal of one or more columns due to the exposure to blast loads. The lack of structural continuity in precast concrete buildings makes these buildings more vulnerable to progressive collapse as compared to the regular cast-in-situ concrete buildings. This study presents experiments involving two types of detailing of precast beam-column joints using half-scale test specimens when the middle column is suddenly removed. The test specimens represent the most prevalent precast beam-column joints. One conventional cast-in-situ test specimen, having continuous top and bottom beam rebars, was used for comparison. The progressive collapse scenario was simulated by removing the central column support and applying a sudden vertical load on this column at a rate of 100 mm/s until failure. Test results helped in developing better understanding about the progressive collapse potential in the existing precast buildings. This study highlights the need for the rehabilitation of beam-column connections in existing precast buildings and necessitates the need for innovative beamcolumn connections for improving the progressive collapse resistance.