M. Neaz Sheikh

Shear and Compressibility Behavior of Sand–Tire Crumb Mixtures

AbstractScrap tire disposal has been a critical environmental problem in many urban cities due to the huge increase in the number of vehicles. Significant research efforts have been devoted in recent years to explore the use of scrap tires in civil engineering application, as reuse or recycling of scrap tires is the preferred option from a waste management perspective. This paper investigates shear and compressibility behavior of sand–tire crumb (S-TC) mixtures for their application in civil engineering projects. Unlike other studies where tire chips or tire shreds were used, shear strength of the S-TC mixtures has been found to decrease with the increase in the amount of tire crumbs in the mixtures. Significant increase in axial strain corresponding to peak deviator stress has been observed. This can be related to the ductility capacity of the mixtures, as confirmed by brittleness tests. It has also been observed that a larger proportion of plastic strain develops after the first cycle of unloading, and ...

Experimental Investigations on Circular Concrete Columns Reinforced with GFRP Bars and Helices under Different Loading Conditions

AbstractGlass-fiber-reinforced polymer (GFRP) bar has emerged as a preferable alternative to steel bar in reinforced concrete (RC) members in harsh, corrosive, coastal environments in order to eliminate corrosion problems. However, only limited experimental studies are available on the performance and behavior of concrete columns reinforced with GFRP bars under different loading conditions. This study investigates the use of GFRP bars and GFRP helices (spirals) as longitudinal and transversal reinforcement, respectively, in RC columns. A total of 12 circular concrete specimens with 205-mm diameter and 800-mm height were cast and tested under different loading conditions. The effect of replacing steel with GFRP reinforcement and changing the spacing of the GFRP helices on the behavior of the specimens was investigated. The experimental results show that the axial load and bending moment capacity of the GFRP-RC columns are smaller than those of the conventional steel-RC columns. However, the ductility of th...

Influence of Rock Depth on Seismic Site Classification for Shallow Bedrock Regions

Seismic site classifications are used to represent site effects for estimating hazard parameters (response spectral ordinates) at the soil surface. Seismic site classifications have generally been carried out using average shear wave velocity and/or standard penetration test n-values of top 30-m soil layers, according to the recommendations of the National Earthquake Hazards Reduction Program (NEHRP) or the International Building Code (IBC). The site classification system in the NEHRP and the IBC is based on the studies carried out in the United States where soil layers extend up to several hundred meters before reaching any distinct soil-bedrock interface and may not be directly applicable to other regions, especially in regions having shallow geological deposits. This paper investigates the influence of rock depth on site classes based on the recommendations of the NEHRP and the IBC. For this study, soil sites having a wide range of average shear wave velocities (or standard penetration test n-values) have been collected from different parts of Australia, China, and India. Shear wave velocities of rock layers underneath soil layers have also been collected at depths from a few meters to 180 m. It is shown that a site classification system based on the top 30-m soil layers often represents stiffer site classes for soil sites having shallow rock depths (rock depths less than 25 m from the soil surface). A new site classification system based on average soil thickness up to engineering bedrock has been proposed herein, which is considered more representative for soil sites in shallow bedrock regions. It has been observed that response spectral ordinates, amplification factors, and site periods estimated using one-dimensional shear wave analysis considering the depth of engineering bedrock are different from those obtained considering top 30-m soil layers.

A new model for the prediction of earthquake ground-motion duration in Iran

The paper proposes a new empirical model to estimate earthquake ground-motion duration, which significantly influences the damage potential of an earthquake. The paper is concerned with significant duration parameters that are defined as the time intervals between which specified values of Arias intensity are reached. In the proposed model, significant duration parameters have been expressed as a function of moment magnitude, closest site-source distance, and site condition. The predictive model has been developed based on a database of earthquake ground-motion records in Iran, containing 286 records up to the year 2007, and a random-effect regression procedure. The result of the proposed model has been compared with that of other published models. It has been found that the proposed model can predict earthquake ground-motion duration in Iran with adequate accuracy.

Experimental Study on FRP Tube Reinforced Concrete Columns under Different Loading Conditions

AbstractThe behavior of fiber-reinforced polymer (FRP) tube reinforced concrete (FTRC) columns under different loading conditions was investigated in this study. Four groups of 16 specimens were cast and tested. Specimens in the first group (the reference group) were reinforced with longitudinal steel bars and steel helices (Group REF). Specimens in the second group were reinforced with intact glass FRP tubes (Group IT). Specimens in the third group were also reinforced with intact glass FRP tubes. In addition, polymer grid was embedded into the concrete cover to reduce the cover spalling (Group ITG). Specimens in the fourth group were reinforced with perforated glass FRP tubes (Group PT). One specimen from each group was tested under concentric loading, one under 25-mm eccentric loading, one under 50-mm eccentric loading, and one under four-point loading. Results from the experimental study show that FRP tubes significantly increase the load-carrying capacity and ductility of FTRC specimens. Group ITG sp...

Liquefaction Potential and Dynamic Properties of Sand-Tyre Chip (STCh) Mixtures

This paper presented the results of the investigations on the liquefaction potential and the dynamic properties of sand-tyre chip (STCh) mixtures. A series of strain controlled consolidated undrained cyclic triaxial tests were carried out on specimens of sand mixed with varying proportions of tyre chips (TCh). The specimens of STCh mixture were prepared at a constant initial relative density and tested at an effective confining pressure of 69 kPa. The results show that TCh significantly reduces the liquefaction potential of sand with the addition of gravimetric proportion of TCh between 20 and 40 % to sand. The maximum shear modulus (Gmax) of the STCh mixture was determined by bender element tests for different gravimetric proportions of TCh and effective confining pressures. The initial shear modulus has been found to be influenced by the proportion of TCh and confining pressure. The shear modulus degradation and damping ratio curves were developed for dynamic analysis of sand-scrap tyre mixtures. The increase of scrap tyre in sand-scrap tyre mixtures reduced the shear modulus degradation and increased the damping ratio.

Load and Moment Interaction Diagram for Circular Concrete Columns Reinforced with GFRP Bars and GFRP Helices

AbstractThis paper presents analytical and experimental studies on the axial load-bending moment behavior of glass fiber–reinforced polymer (GFRP) bars and helices RC columns. The nominal axial load and bending moment of the columns were analyzed based on the stress-strain behavior of the cross-sectional components. A numerical integration method was used to determine the compressive force of concrete in the compression region. The analytical results were verified with experimental results of 12 circular specimens reinforced with GFRP bars and GFRP helices. Out of these 12 specimens, eight specimens were taken from available literature and four specimens were tested in this study. The influences of different parameters such as loading conditions, spacing of the GFRP helices, and wrapping the specimens with carbon fiber–reinforced polymer (CFRP) sheets on the behavior of GFRP-RC specimens were investigated. A parametric study was also carried out to investigate the effects of longitudinal and transverse GF...

Behavior of Circularized Hollow RC Columns under Different Loading Conditions

AbstractOne of the methods for strengthening square concrete columns is shape modification. The method involves modification of the column cross section from square to circular by bonding concrete ...

Behavior of Self-Compacting Concrete Columns Reinforced Longitudinally with Steel Tubes

AbstractThis study investigates the behavior of self-compacting concrete (SCC) specimens reinforced with small-diameter steel tubes in lieu of reinforcing bars. Twenty specimens were cast and teste...

Axial-flexural interactions of GFRP-CFFT columns with and without reinforcing GFRP bars

AbstractThis study presents the results of an experimental program and analytical modeling for axial-flexural interactions of concrete-filled glass fiber–reinforced polymer tube (GFRP-CFFT) columns...