The most critical drawback in currently used steel reinforcement in reinforced concrete (RC) structures is susceptibility to accumulation of plastic deformation under excessive loads. Many concrete structures due to damaged (yielded) steel reinforcement have undergone costly repairs and replacements. This research presents a new type of shape memory alloy (SMA)-based composite reinforcement with ability to withstand high elongation while exhibiting pseudo-elastic behavior. In this study, small diameter SMA wires are embedded in thermoset resin matrix with or without additional glass fibers to develop composite reinforcement. Manufacturing technique of new proposed composite is validated using microscopy images. The proposed SMA-FRP composite square rebars are first fabricated and then embedded in small scale concrete T-beam. 3-point bending test is conducted on manufactured RC beam using a cyclic displacement controlled regime until failure. It is found that the SMA-FRP composite reinforcement is able to enhance the performance of concrete member by providing re-centering and crack closing capability.
The concept of structural robustness and relevant design guidelines have been in existence in the progressive collapse literature since the 1970s following the partial collapse of the Ronan Point apartment building; however, in the more general context, research on the evaluation and enhancement of structural robustness is still relatively limited. This paper is aimed to provide a general overview of the current state of research concerning structural robustness. The focus is placed on the quantification and the associated evaluation methodologies, rather than specific measures to ensure prescriptive robustness requirements. Some associated concepts, such as redundancy and vulnerability, will be discussed and interpreted in the general context of robustness such that the corresponding methodologies can be compared quantitatively using a comparable scale. A framework methodology proposed by the authors is also introduced in line with the discussion of the literature.
In the framework of finite element meshes, a novel continuous/discontinuous deformation analysis (CDDA) method is proposed in this paper for modeling of crack problems. In the present CDDA, simple polynomial interpolations are defined at the deformable block elements, and a link element is employed to connect the adjacent block elements. The CDDA is particularly suitable for modeling the fracture propagation because the switch from continuous deformation analysis to discontinuous deformation analysis is natural and convenient without additional procedures. The SIFs (stress intensity factors) for various types of cracks, such as kinked cracks or curved cracks, can be easily computed in the CDDA by using the virtual crack extension technique (VCET). Both the formulation and implementation of the VCET in CDDA are simple and straightforward. Numerical examples indicate that the present CDDA can obtain high accuracy in SIF results with simple polynomial interpolations and insensitive to mesh sizes, and can automatically simulate the crack propagation without degrading accuracy.
Corrosion of reinforced concrete (RC) structures is one of the significant causes of deterioration of reinforced concrete (RC) structures. Chlorination is a major process governing the initiation and advancement of the injurious corrosion of steel bars. Now, several researches on the chlorination of concrete structures have been ongoing around the world. Present article reviews several recently performed chlorination studies, and from results of a field survey evaluates the effect of chloride content on the probability of corrosion and the influence of concrete compressive strength on the chloride content and penetration, also evaluates the effect of concrete cover over the chloride content of the RC structures at rebar depth and on the probability of corrosion.
The responses of cement mortar specimens of different dimensions under compression and tension were calculated based on the discrete element method with the modified-rigid-body-spring concrete model, in which the mechanical parameters derived from macro-scale material tests were applied directly to the mortar elements. By comparing the calculated results with those predicted by the Carpinteri and Weibull size effects laws, a series of formulas to convert the macro-scale mechanical parameters of mortar and interface to those at the meso-scale were proposed through a fitting analysis. Based on the proposed formulas, numerical simulation of axial compressive and tensile failure processes of concrete and cement mortar materials, respectively were conducted. The calculated results were a good match with the test results.
This paper reviews wind loading codes and standards in the Asia-Pacific Region, in particular in the 15 countries and areas. A general description of wind loading model is given as a famous wind loading chain described by four variables including velocity pressure, exposure factor, pressure coefficient, and gust response factor. Through the APEC-WW Workshops and the extensive calculations for three examples of low, medium and high rise buildings, these four important variables of wind loads are evaluated and compared with statistical parameters, mean values and coefficients of variation. The main results of the comparison show some differences among the 15 economies, and the reasons and further incorporation are discussed and suggested.
With increasing environmental pressure to reduce solid waste and to recycle as much as possible, the concrete industry has adopted a number of methods to achieve this goal by replacement of waste glass with concrete composition materials. Due to differences in mixture design, placement and consolidation techniques, the strength and durability of Self Compacting Concrete (SCC) may be different than those of conventional concrete. Therefore, replacement of waste glass with fine aggregate in SCC should deeply be investigated compared to conventional concretes. The aim of the present study is to investigate the effect of glass replacement with fine aggregate on the SCC properties. In present study, fine aggregate has been replaced with waste glass in six different weight ratios ranging from 0% to 50%. Fresh results indicate that the flow-ability characteristics have been increased as the waste glass incorporated to paste volume. Nevertheless, compressive, flexural and splitting strengths of concrete containing waste glass have been shown to decrease when the content of waste glass is increased. The strength reduction of concrete in different glass replacement ratios is not remarkable, thus it can be produced SCC with waste glass as fine aggregate in a standard manner.
The present study focuses on the improvement of pozzolanic reaction of fly ash particles with the cement hydration products. Low and high volume fly ash concrete mixtures were studied systematically with the addition of accelerating admixtures and accelerated curing of the concrete specimens in a steam chamber for 18 h at 75°C. Also, the reinforcing effects of glued steel fibers addition on the compressive and flexural performance of fly ash concrete were investigated. The test results indicated that the addition of accelerator improved the rate of hardening and the inclusion of steel fibers provided higher flexural performance. Also, it can be noted that the high volume fly ash (50%) addition in concrete showed a reduction in strength; however, the addition of accelerator has compensated the deceleration in strength gain. The proper selection of concrete ingredients, addition of accelerator and initial steam curing for 18 h showed better improvement on the engineering properties in fly ash concrete. A maximum increase (41.7%) in compressive strength of fly ash concrete around 52.90 MPa was noticed for 25% fly ash substitution and 1.5% steel fibers addition. Dynamic elastic modulus was also calculated in loaded concrete specimen using ultrasonic pulse velocity test and showed a good agreement with the experimental value.
An estimate of the ultimate load on foundations on soil layers subject to groundwater flow has been presented. The kinematic approach of the limit analysis was employed to find the upper-bound limit of the bearing capacity. Both smooth and rough base strip foundations were considered associated with different collapse patterns. Presence of the groundwater flow leads to a non-symmetric collapse pattern, i.e., a weak side and a strong side in two-sided collapse patterns, depending on the direction of the flow. It was found that the bearing capacity has a decreasing trend with increase in the groundwater flow gradient and hence, a reduction factor has been introduced to the third term in the bearing capacity equation as a function of the flow gradient.
Understanding the effects of land use change on the hydrological cycle is very important for development of sustainable water resource in an upland field catchment. In this study, soil and hydrological properties in an upland field catchment, which was reclaimed partially from a forest catchment, were compared with another forest catchment. The soil properties of surface and subsurface layers were investigated in the two catchments. The soil was compacted and water-holding capacity of soil in the upland field catchment became smaller after the reclamation from forest to upland field, which decreased infiltration rate and water storage in the soil layers. We found that peak discharge and direct runoff in the upland field catchment increased compared with the forest catchment. Annual evapotranspiration from the upland field catchment tended to be lower due to the change in vegetation type and soil properties. Furthermore, a semi-distributed hydrological model was applied in the upland field catchment to understand the integrated effects of reclamation on the hydrological cycle. The model parameters, which were determined using a nonlinear optimization technique—the Shuffled Complex Evolution method (SCE), were compared between the two catchments. The Nash and Sutcliffe coefficient was used to evaluate the model performance. The simulated results indicated that evapotranspiration was decreased and change in discharge was more obvious in the surface layer. We considered that declined infiltration and water storage and increased peak discharge and direct runoff have a negative impact on water resources in the upland field catchment. This study will provide information for forest managers in planning and making decisions for land and water resource management.
Cold-formed steel members, which experience complicated prestrain histories, are frequently applied in structural engineering. This paper aims to predict cyclic plasticity of structural steels with tensile and compressive prestrain. Monotonic and cyclic tests on hourglass specimens with tensile and compressive prestrain are conducted, and compared with numerical simulations using the Chaboche model. Two approaches are taken in the simulation. The first requires only the monotonic tensile test data from the prestrained steels, and the second requires both the monotonic tensile test data from the virgin steel and the prestrain histories. The first approach slightly overestimates the compressive stress for specimens with tensile prestrain, while the second approach is able to accurately predict the cyclic plasticity in specimens with tensile and compressive prestrain.