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CONTENTS
Volume 7, Number 1, February 2019
 

Abstract
The conventional ACI rectangular stress block is developed on the basis of normal-strength concrete column tests and it is still being used for the design of high-strength concrete members. Many research papers found in the literature indicate that the nominal strength of high-strength concrete members appears to be over-predicted by the ACI rectangular stress block. This is especially true for HSC columns. The general shape of the stress-strain curve of high-strength concrete becomes more likely as a triangle. A triangular stress block is, therefore, introduced in this paper. The proposed stress block is verified using a database which consists of 52 tested singly reinforced high-strength concrete beams having concrete strength above 55 MPa (8,000 psi). In addition, the proposed model is compared with models of various design codes and proposals of researchers found in the literature. The nominal flexural strengths computed using the proposed stress block are in a good agreement with the tested data as well as with that obtained from design codes models and proposals of researchers.

Key Words
beams; flexural strength; high-strength concrete; triangular stress block

Address
Mustafa Kamal Al-Kamal: Department of Civil Engineering, Al-Nahrain University, Baghdad, Iraq

Abstract
A comprehensive assessing approach for durability of reinforced concrete structures dealing with the corrosion process of rebar subjected to the attack of aggressive agent from environment was proposed in this paper. Corrosion of rebar was suggested in the form of combination of global corrosion and pitting. Firstly, for the purposed of considering the influence of rebar\'s radius, a type of Plane Corrosion Model (PCM) based on uniform corrosion of rebar was introduced. By means of FE simulation approach, global corrosion process of rebar regarding PCM and LCM (Linear Corrosion Model) was regressed and compared according to the data from Laboratoire Matériaux et Durabilite des Constructions (LMDC). Secondly, pitting factor model of rebar in general descend law with corrosion degree was introduced in terms of existing experimental data. Finally, with the comprehensive numerical simulation, the durability of an existing arch bridge was studied in depth in deterministic way, including diffusion process and sectional strength of typical cross section of arch, crossbeam and deck slab. Evolution of structural capacity considering life-cycle rehabilitation strategy indicated the degradation law of durability of reinforced arch bridges.

Key Words
reinforced concrete structures; diffusion; corrosion; durability; service life

Address
Xuhong Zhou, Xi Tu: Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, Chongqing, China
Airong Chen: Department of Bridge Engineering, Tongji University, Shanghai, China
Yuqian Wang: China-Road Transportation Verification & Inspection Hi-Tech Co. Ltd., Beijing, China

Abstract
Five key items were used to create an economical and physically small impact test device for concrete panels subject to high speed collision: an air-compressive system, carbon steel pipe, solenoid valve, carrier and carrier-blocking, and velocity measurement device. The impact test device developed can launch a 20 mm steel spherical projectile at over 200 m/s with measured impact and/or residual velocity. Purpose for development was to conduct preliminary materials tests, prior to large-scale collision experiments. In this paper, the design process of the small impact test device was discussed in detail.

Key Words
small impact test device; impact resistance; high speed collision; concrete panel

Address
Sanghee Kim, Seung Yong Jeong and Thomas H.-K. Kang: Department of Architecture and Architectural Engineering, Seoul National University, Seoul, 08826, Korea

Abstract
This paper evaluates the workability and hardened properties of self-compacting concrete (SCC) containing silica fume as the partial replacement of cement. SCC mixtures with 0, 2, 4, 6, 8 and 10% silica fume were tested for fresh and hardened properties. Slump flow with T500 time, L-box and V-funnel tests were performed for evaluating the workability properties of SCC mixtures. Compressive strength, splitting tensile strength and modulus of rupture were performed on hardened SCC mixtures. Experiments revealed that replacement of cement by silica fume equal to and more than 4% reduced the slump flow diameter and increased the T500 and V-funnel time linearly. Compressive strength, splitting tensile strength and modulus of rupture increased with increasing the replacement level of cement by silica fume and were found to be maximum for SCC mixture with 10% silica fume. Further, residual hardened properties of SCC mixture yielding maximum strengths (i.e., SCC with 10% silica fume) were determined experimentally after heating the concrete samples up to 200, 400, 600 and 800oC. Reductions in hardened properties up to 200oC were found to be very close to normal vibrated concrete (NVC). For 400 and 600oC reductions in hardened properties of SCC were found to be more than NVC of the same strength. Explosive spalling occurred in concrete specimens before reaching 800oC.

Key Words
self-compacting concrete; silica fume; mechanical properties; elevated temperature

Address
Subhan Ahmad, Arshad Umar, Amjad Masood and Mohammad Nayeem: Department of Civil Engineering, Aligarh Muslim University, Aligarh, India

Abstract
This study presents a comprehensive experimental investigation on mostly encountered types of Reinforced Concrete Haunched Beams (RCHBs) where three modes of RCHBs investigated; the diversity of studied beams makes it a pioneer in this topic. The experimental study consists of twenty RCHBs and four prismatic beams. Effects of important parameters including beam type, the inclination angle, flexure and compressive reinforcement, shear reinforcement on mechanical behavior and failure mode of each mode of RCHBs were examined in detail. Furthermore crack propagation at certain load levels were inspected and visualized for each RCHB mode. The results confirm that RCHBs have different behavior in shear as compared to the prismatic beams. At the same time, different mechanical behavior was observed between the modes of RCHBs. Therefore, RCHBs were classified into three modes according to the inclination shape and mode of failure (Modes A, B and C). However, it was observed that there is no significant difference between RCHBs and prismatic beams regarding flexural behavior. Moreover, a new and unified formula was proposed to predict the critical effective depth of all modes of RCHBs that is very useful to predict the critical section for failure.

Key Words
Haunched beams; load capacity; load-deflection curve; failure mode; crack propagation

Address
Hasan M. Albegmprli: Engineering Technical College, Building and Construction Engineering Department, Northern Technical University, Mosul, Iraq
M. Eren Gülşan and Abdulkadir Cevik: Civil Engineering Department, Gaziantep University, University Avenue - Central Campus, Gaziantep, Turkey

Abstract
The project focuses on the dynamic analysis of concrete beams reinforced with silica-nanoparticles under blast loading. The structure is located at two boundary conditions. The equivalent composite properties are determined using Mori-Tanak model. The structure is simulated with sinusoidal shear deformation theory. Employing nonlinear strains-displacements, stress-strain, the energy equations of beam were obtained and using Hamilton

Key Words
dynamic analysis; concrete beam; DQM; silica nanoparticle

Address
Masoud Azmi, Reza Kolahchi and Mahmood Rabani Bidgoli: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran


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