International Journal of Concrete Structures and Materials

This paper reports the results of a seismic performance study of a precast shear wall with a new horizontal connection. The new connection is the rabbet-unbonded horizontal connection, which is composed of rabbets and unbonded rebar segments. The rabbets are used to improve the shear capacity and prevent slippage of the connection, and the unbonded rebar segments are used to improve the ductility and energy dissipation. Three specimens were tested with different parameters under cyclic quasi-static loading. The test results showed that the specimen with a larger unbonded level had a richer hysteresis curve, larger ductility, larger energy dissipation, and slightly smaller bearing capacity. Moreover, in relation to the stiffness degradation, in the initial stage, the specimen with a larger unbonded level had a smaller stiffness, whereas in the last stage, the stiffnesses were similar regardless of the unbonded level. A parameter analysis using a finite element model proved that the ductility and energy dissipation of a shear wall with the rabbet-unbonded horizontal connection increased with the unbonded length and level. In addition, when the axial compression ratio increased, the bearing capacity increased, but the load–displacement curves decreased more rapidly. It was concluded that the unbonded length and unbonded level could effectively improve the ductility and energy dissipation of a shear wall. However, they should not be too large under high pressure, and the design suggestions for the new connection need further research considering other factors.

Reinforced concrete (RC) beams strengthened by externally bonded reinforcement often fail by debonding. This paper presents an experimental and analytical study aimed at better understanding and modeling the fiber reinforced polymer (FRP) debonding failures in strengthened RC beams under monotonic and cyclic loads. In order to investigate the flexural behavior and failure modes of FRP-strengthened beams under monotonic and cyclic loadings, an experimental program was carried out. An analytical study based on the energy balance of the system was also performed. It considers the dominant mechanisms of energy dissipation during debonding and predicts the failure load of the strengthened beams. Validation of the model was carried out using test data obtained from the own experimental investigation.

In this study, portland cement (PC) has been partially replaced with a Class F fly ash (FA) at level of 70 % to produce high-volume FA (HVFA) concrete (F70). F70 was modified by replacing FA at levels of 10 and 20 % with silica fume (SF) and ground granulated blast-furnace slag (GGBS) and their equally combinations. All HVFA concrete types were compared to PC concrete. After curing for 7, 28, 90 and 180 days the specimens were tested in compression and abrasion. The various decomposition phases formed were identified using X-ray diffraction. The morphology of the formed hydrates was studied using scanning electron microscopy. The results indicated higher abrasion resistance of HVFA concrete blended with either SF or equally combinations of SF and GGBS, whilst lower abrasion resistance was noted in HVFA blended with GGBS.

The process of selecting a repair material is a typical one of multi-criteria decision-making (MCDM) problems. In this study Analytical Hierarch Process was applied to solve this MCDM problem. Many factors affecting a process to select an optimal repair material can be classified into quantitative and qualitative requirements and this study handled only quantitative items. Quantitative requirements in the optimal selection model for repair material were divided into two parts, namely, the required chemical performance and the required physical performance. The former is composed of alkali-resistance, chloride permeability and electrical resistivity. The latter is composed of compressive strength, tensile strength, adhesive strength, drying shrinkage, elasticity and thermal expansion. The result of the study shows that this method is the useful and rational engineering approach in the problem concerning the selection of one out of many candidate repair materials even if this study was limited to repair material only for chloride-deteriorated concrete.

The aim of this work is to propose a technique to calculate the strength of short concrete-filled steel tube columns under the short-term action of a compressive load, based on the phenomenological approach and the theoretical positions of reinforced concrete mechanics. The main dependencies that allow the realization of the deformation calculation model in practice are considered. A distinctive feature of the proposed approach is the method of the multipoint construction of deformation diagrams for a concrete core and steel shell. In this case, two main factors are taken into account. First, the steel shell and the concrete core work under conditions of a complex stress state. Since the proposed dependencies to determine the strength and the ultimate relative strain of volumetrically compressed concrete are obtained phenomenologically, they are more versatile than the commonly used empirical formulas. In particular, they can be used for self-stressing, fine-grained and other types of concrete. Second, with a step-by-step increase in the relative deformation, the lateral pressure on a concrete core and a steel shell constantly change. Thus, the parametric points of the concrete and steel deformation diagrams also change at each step. This circumstance was not taken into account in earlier calculations. A comparison of the theoretical and experimental results indicates that the practical application of the developed calculation procedure gives a reliable and fairly stable estimate of the stress–strain state and the strength of concrete-filled steel tube columns.

The volume fraction of the coarse aggregate in the conventional plastic concrete is controlled relatively low to ensure a required workability. In this paper, a new type of coarse aggregate interlocking concrete with strength ranging from C30 to C80 was prepared with scattering-filling aggregate process. The strength of concrete prepared with this method increases obviously whereas the shrinkage decreases significantly, the cement dosage in the concrete decreased 20 % at the same time. The micro-hardness of the ITZ between the cement paste and scattering-filling aggregate is higher than that of the original aggregate, the ITZ become narrower and tighter also. The interlocking and more even distribution of the coarse aggregate and the water absorption of the addition of extra amount of coarse aggregates contribute to the strength and performance improvement of the concrete prepared with scattering-filling aggregate process.

In recent years, constructing natural aggregates as a base layer for the roads has increased. Natural resources will run out as long as human consumption of them continues. Recycled concrete aggregate (RC) has thus emerged as a substitute material for the building of road base layers. Additionally, RC can be utilized to create interior city highways. The base layer for roads must have sufficient strength to support the working load on the pavement surface without damage deforming. As a result, the focus of this paper is on enhancing the structural performance of sandy soil reinforced with various RC percentages. The three key factors are relative soil density (Dr = 83 and 97%), recycled concrete aggregate reinforcing levels (RC = 0,5,10,15,20,25,30,40,50 and 100%), and reinforcement layer thickness (Rd = 0.0B, 0.5B, B, and 2B where B is the footing model width). Numerous laboratory experiments were conducted in order to examine the impact of important parameters on the properties of the mixtures. The plate bearing tests were carried out using a footing model (250 × 250 mm) inside a tank (1500 × 1500x1000 mm) to ascertain the stress–strain response, bearing capacity ratio (BCR), ultimate bearing capacity, and modulus of elasticity of the tested mixtures. It is clear that raising the RC has no effect on the diameters of the grains. It was found that as RC increased, the mixture's bulk density increased but specific gravity decreased. Maximum dry density rose as RC rose, whereas water content fell. It was noted that BCR unquestionably increased as RC increased for all RC levels and all values of settlement ratios. The appropriate reinforcing layer thickness is suggested to be no more than 2B. As the RC concentration in the sand and Rd increased, the difference between two pressure-settlement curves of densities 83% and 97% significantly decreased. Furthermore, when RC reaches 50%, two curves are roughly comparable. At RC = 50%, it is advised that the relative density of 83% is sufficient to produce the same behavior as the relative density of 97%. It was found that as RC and Rd grew, the tested mixtures' ultimate bearing capacity and elasticity modulus increased as well. A novel proposed formulas are developed to compute bearing capacity ratio, ultimate bearing capacity, and elasticity modulus of the tested mixtures taking into account the influence of RC, reinforcement layer depth, settlement ratio, and the relative density, and its results agree with the experimental results.

In this paper, a new approach is developed to numerically evaluate the structural performance of deteriorated prestressed concrete beams using the finite element analysis application RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology). A prestressing steel element was modified to represent the interaction between deteriorated concrete and prestressing steel. Considering the corrosion effects—as shown by the reduction of the prestressing steel section and loss of bond—a nonlinear material model was proposed for deteriorated prestressed concrete behavior. The modified damage index is intended to provide a numerical method for quantifying the structural performance of deteriorated prestressed concrete beams. The analytical procedure developed for the performance evaluation of deteriorated beams was validated by comparison with the credible test results, thereby enabling a more reliable and rational prestressed concrete beams design process.

Sự căng thẳng nhiệt trong công trình bê tông khối tương đối cao trong quá trình thi công, thường dẫn đến việc xuất hiện nứt do nhiệt. Để giải quyết vấn đề này, các khối bê tông thường được đặt bằng cách tạo ra các rãnh rộng. Việc kết nối các thanh thép bị cắt tại vị trí các rãnh rộng bằng cách hàn hoặc ép ống có nhiều nhược điểm. Để khắc phục vấn đề mất mát ứng lực do nhiệt, bài báo này đề xuất một loại thanh thép HRB400 có dạng cung nhẹ (SCAHRB400) mà không cần cắt đứt các thanh thép. Các thử nghiệm kéo và mô phỏng số đã được thực hiện cho năm loại thanh thép SCAHRB400 với sự xem xét về phi tuyến hình học và vật liệu. Dựa trên kết quả thử nghiệm và mô phỏng số, mối quan hệ tương đương giữa ứng suất và biến dạng của thanh thép SCAHRB400 đã được thiết lập, và sự xuất hiện của vùng dẻo của thanh thép SCAHRB400 trong quá trình kéo đã được quan sát, các đặc tính kéo của thanh thép SCAHRB400 đã được phân tích và thảo luận. Kết quả thử nghiệm cho thấy rằng các thanh thép SCAHRB400 có xu hướng bị nhún cục bộ gần chóp của các vòm lớn và tại vị trí kết nối giữa các phần ngang và cong. Các đường cong ứng suất–biến dạng tương đương trong mô phỏng số có quy luật rõ ràng. Các đường cong ứng suất–biến dạng của thanh thép HRB400 có dạng cung nhẹ và HRB335 có quy luật biến đổi tương tự. Khi ứng suất nhỏ, độ cứng kéo và độ cứng nén trục của thanh thép HRB400 có dạng cung nhẹ và HRB335 là tương tự; khi ứng suất lớn, độ cứng trục của thanh thép SCAHRB400 lớn hơn so với thanh thép HRB335 có dạng cung nhẹ. Qua các nghiên cứu thử nghiệm và mô phỏng số, cơ sở lý thuyết có thể được thiết lập cho ứng dụng kỹ thuật của các thanh thép có dạng cung nhẹ mới trong bê tông khối.

This paper presents results of an experimental investigation on the behaviour of bond between external glass fibre reinforced polymer reinforcement and concrete exposed to three different environmental conditions, namely, temperature cycles, wet–dry cycles and outdoor environment separately for extended durations. Single shear tests (pull-out test) were conducted to investigate bond strengths (pull-out strengths) of control (unexposed) and exposed specimens. Effect of the exposure conditions on the compressive strength of concrete were also investigated separately to understand the effect of changing concrete compressive strength on the pull-out strength. Based on the comparison of experimental results of exposed specimens to control specimens in terms of bond strengths, failure modes and strain profiles, the most significant degradation of pull-out strength was observed in specimens exposed to outdoor environment, whereas temperature cycles did not cause any deterioration of strength.