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CONTENTS
Volume 29, Number 5, May 2022
 

Abstract
The seismic analytic collapse fragility of soil nail wall structures with a shotcrete concrete covering is investigated in this paper. The finite element modeling process has been well described. The fragility function evaluates the link between ground motion intensities and the likelihood of reaching a specific level of damage. The soil nail wall has been subjected to incremental dynamic analysis (IDA) from medium to strong ground vibrations. The nonlinear dynamic analysis of the soil nail wall uses a set of 20 earthquake ground motions with varying PGAs. PGD is utilized as an intensity measure, the numerical findings demonstrate that the soil nailing wall reaction is particularly sensitive to earthquake intensity measure (IM).

Key Words
finite element modeling; nonlinear time history analysis; soil modeling; soil nail wall structures

Address
Mahmoud Bayat: Department of Civil and Environmental Engineering, University of South Carolina, Columbia SC, USA
Amin Emadi: Department of Civil Engineering, Pajoohesh Consulting Engineers, Tehran, Iran
Amir Homayoun Kosariyeh: Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran
Mehdi Kia: Department of Civil Engineering, University of Science and Technology of Mazandaran, Behshahr, Iran
Mahdi Bayat: Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran

Abstract
This study aims at developing a torsional strength model based on a nonlinear analysis method presented in the previous studies. To this end, flexural neutral axis depth of a reinforced concrete section and effective thickness of an idealized thin-walled tube were formulated based on reasonable approximations. In addition, various sectional force components, such as shear, flexure, axial compression, and torsional moment, were considered in estimating torsional strength by addressing a simple and linear strain profile. Existing test results were collected from literature for verifications by comparing with those estimated from the proposed model. On this basis, it can be confirmed that the proposed model can evaluate the torsional strength of RC members subjected to combined loads with a good level of accuracy, and it also well captured inter-related mechanisms between shear, bending moment, axial compression, and torsion.

Key Words
combined loads; multi-potential capacity; reinforced concrete; strain effect; torsional strength

Address
Hyunjin Ju: School of Architecture and Design Convergence, Hankyong National University, 327 Jungang-ro, Anseong, Gyeonggi 17579, Korea
Deuckhang Lee: Department of Architectural Engineering, Chungbuk National University, 1 Chungdae-ro, Seowon-gu, Cheongju, Chungbuk 28644, Korea
Wei Zhang: Department of Architectural Engineering, Chungbuk National University, 1 Chungdae-ro, Seowon-gu, Cheongju, Chungbuk 28644, Korea
Lei Wang: School of Civil Engineering, Changsha University of Science and Technology, 960 Wanjiali Road, Changsha, Hunan 410114, China

Abstract
The current design equations for predicting the torsional capacity of RC members underestimate the torsional strength of under-reinforced members and overestimate the torsional strength of over-reinforced members. This is because the design equations consider only the yield strength of torsional reinforcement and the cross-sectional properties of members in determining the torsional capacity. This paper presents an analytical model to predict the thickness of shear flow path in RC beams subjected to pure torsion. The analytical model assumes that torsional reinforcement resists torsional moment with a sufficient deformation capacity until concrete fails by crushing. The ACI 318 code is modified by applying analytical results from the proposed model such as the average stress of torsional reinforcement and the effective gross area enclosed by the shear flow path. Comparison of the calculated and observed torsional strengths of existing 129 test beams showed good agreement. Two design variables related to the compressive strength of concrete in the proposed model are approximated for design application. The accuracy of the ACI 318 code for the over-reinforced test beams improved somewhat with the use of the approximations for the average stresses of reinforcements and the effective gross area enclosed by the shear flow path.

Key Words
average stress; cracked concrete; shear flow path; torsional reinforcement; torsional strength

Address
Hyeong-Gook Kim: Department of Architectural and Urban System Engineering, Kongju National University, Cheonan 31080, Korea
Jung-Yoon Lee: School of Civil and Architectural Engineering, Sungkyunkwan University, Suwon 16419, Korea
Kil-Hee Kim: Department of Architectural and Urban System Engineering, Kongju National University, Cheonan 31080, Korea

Abstract
In order to study the axial compression performance of basalt-fiber reinforced recycled concrete (BFRRC) filled circular steel tubular short columns, the axial compression performance tests of seven short column specimens were conducted to observe the mechanical whole-process and failure mode of the specimens, the load-displacement curves and the load-strain curves of the specimens were obtained, the influence of design parameters on the axial compression performance of BFRRC filled circular steel tubular short columns was analyzed, and a practical mathematical model of stiffness degradation and a feasible stress-strain curve equation for the whole process were suggested. The results show that under the axial compression, the steel tube buckled and the core BFRRC was crushed. The load–axial deformation curves of all specimens show a longer deformation flow amplitude. Compared with the recycled coarse aggregate (RCA) replacement ratio and the basalt fiber dosage, the BFRRC strength has a great influence on the peak bearing capacity of the specimen. The RCA replacement ratio and the BFRRC strength are detrimental to ductility, whereas the basalt fiber dosage is beneficial to ductility.

Key Words
axial compression; basalt fiber; circular steel tube; mechanical properties; recycled aggregate concrete; stress-strain curve

Address
Xianggang Zhang: School of Intelligent Construction, Wuchang University of Technology, Wuhan 430223, China; School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454003, China
Songpeng Zhang: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454003, China; Zhejiang Geophysical Technology Application Research Institute Co., Ltd., Hangzhou 310000, China
Xu Chen: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454003, China
Xiang Gao: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454003, China
Chunheng Zhou: School of Civil and Environmental Engineering, Ningbo University, Ningbo 315211, China

Abstract
Geopolymers are an important alternative material supporting recycling, sustainability, and waste management. Durability properties are among the most critical parameters to be investigated; in this study, the durability of manufactured geopolymer samples under the attack of 10% magnesium sulfate and 10% sodium sulfate solution was investigated. 180 cycles of freezing and thawing were also tested. The experimentally obtained results investigate the durability of geopolymer mortar prepared with fly ash (class F) and alkali activator. Three different quarry dust wastes replaced the river sand aggregate: limestone, marble, and basalt powder as fine filler aggregate in three different replacement ratios of 25%, 50%, and 75% to produce ten series of geopolymer composites. The geopolymer samples' visual appearance, weight changes, UPV, and strength properties were studied for up to 12 months at different time intervals of exposure to sulfate solutions to investigate sulfate resistance. In addition, Scanning Electron Microscopy (SEM), EDS, and XRD were used to study the microstructure of the samples. It was beneficial to include quarry waste as a filler aggregate in durability and mechanical properties. The compact matrix was demonstrated by microstructural analysis of the manufactured specimens. The geopolymer mortars immersed in sodium sulfate showed less strength reduction and deterioration than magnesium sulfate, indicating that magnesium sulfate is more aggressive than sodium sulfate. Therefore, it is concluded that using waste dust interrogation with partial replacement of river sand with fly ash-based geopolymers has satisfactory results in terms of durability properties of freeze-thaw and sulfate resistance.

Key Words
durability; fly ash; freezing-thawing; geopolymer; microstructure; quarry waste materials; sulfate environment

Address
Yosra Tammam: Civil Engineering Department, Istanbul Gelisim University, Istanbul, Turkey
Mucteba Uysal: Civil Engineering Department, Faculty of Civil Engineering, Yildiz Technical University, Davutpasa Campus, Istanbul, Turkey
Orhan Canpolat: Civil Engineering Department, Faculty of Civil Engineering, Yildiz Technical University, Davutpasa Campus, Istanbul, Turkey

Abstract
Fiber-reinforced cementitious composites (FRCC) have emerged as a response to the calls for strong, ductile and sustainable concrete mixes. FRCC has shown outstanding mechanical properties and ductility where special fibres are used in the mixes to give it the strength and the ability to exhibit strain hardening. With the possibility of designing the FRCC mixes to include sustainable constituents and by-products materials such as fly ash, FRCC started to emerge as a green alternative as well. To be able to design mixes that achieve these conflicting properties in concrete, there is a need to understand the composition effect on FRCC and optimize these compositions. Therefore, this paper aims to investigate the influence of FRCC compositions on the properties of fresh and hardened of FRCC and then to optimize these mix compositions using factorial design approach. Three factors, water-to-binder ratio (w/b), mineral admixtures (total of fly ash and metakaolin by cement content (MAR)), and metakaolin content (MK), were investigated to determine their effects on the properties of fresh and hardened FRCC. The results show the importance of combining both FA and MK in obtaining a satisfactory fresh and mechanical properties of FRCC. Models were suggested to elucidate the role of the studied factors and a method for optimization was proposed.

Key Words
fiber-reinforced cementitious composites (FRCC); fly ash; metakaolin; optimization; PVA fibres

Address
Mohammed Sonebi:School of Natural and Built Environment, Queen's University Belfast, David Keir Building Stranmillis Road, Belfast, BT9 5AG, United Kingdom
Ahmed Abdalqader: Engineering Department, Tracey Concrete Ltd, Old Rossorry, Sligo Road, Enniskillen BT74 7LF, United Kingdom
Tahreer Fayyad: Engineering Department, Tracey Concrete Ltd, Old Rossorry, Sligo Road, Enniskillen BT74 7LF, United Kingdom
Sofiane Amziane: Civil Engineering Department, University of Clermont Auvergne, Institut Pascal, Campus Universitaire
des Cézeaux, 4 Avenue Blaise Pascal, TSA 60026/CS 60026, 63178 Aubière Cedex, France
Jamal El-Khatib: Civil Engineering Department, Beirut Arab University, Debbieh Main Road, Beirut, Lebanon

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