International Concrete Abstracts Portal

This paper examines the inaccuracy of the initial strain method that is generally adopted in 3D finite element prestressing analysis and discusses the merits of a newly developed method to calculate 3D prestressing effects. The new method considers friction loss of the tendon force as well as pseudo-centripetal forces, allowing a wide range of functional forms for the prestressed concrete (PC) steel force distribution assumption. This study examined the basic concepts for adopting the functional form of the PC steel force distribution at the prestressing and seating stages, after which the observed and calculated values of pulled-out lengths of PC steel were compared to assure the credibility of the assumed functional form of the PC steel force distribution. A three-span continuous bridge model was used to compare results obtained by the conventional method and the new 3D method. The equilibrium of a free body was used also to evaluate the accuracy of results by the new method. The importance of the new method being able to calculate a pulled-out PC steel length considering concrete deformation was stressed because this value may be adopted to confirm assumptions of the PC steel force distribution.

The behavior of carbon fiber-reinforced polymer (CFRP) flexural strengthened reinforced concrete beams under reversed cyclic loading has not been sufficiently studied. In this paper, normal strength concrete is used, with a typical steel ratio (0.5%), to build full-scale rectangular beams strengthened on top and bottom with flexural unanchored and anchored CFRP sheets. Five identical beams were examined under fully reversed cycles up to failure following the AC 125 displacement loading protocol. The first beam was tested as an un-strengthened control specimen. The second and third beams were tested as strengthened specimens using thin sheets with and without fiber anchors. On the other hand, the fourth and fifth beams were tested when strengthened using thick sheets with and without fiber anchors. Specimens with thin sheets underwent higher ductility and lower hysteresis pinching relative to the thick ones. The results are comparatively discussed and compared to a phenomenological cyclic analysis model showing promising correspondence.

Portland cement has played a significant role in the construction of major infrastructure and building structures. However, in light of the substantial CO₂ emissions associated with its production, there is a growing concern about environmental issues. Accordingly, the development of eco-friendly alternatives is actively underway. Geopolymer represents a class of inorganic polymers formed via a chemical interaction between solid aluminosilicate powder with alkali hydroxide and/or alkali silicate compounds. Concrete made with geopolymers, as an alternative to Portland cement, generally demonstrates comparable physical and durability characteristics to ordinary Portland cement concrete (OPC). Research on the material properties of geopolymer concrete (GPC) has made extensive progress. However, the number of large-scale tests that were conducted to assess its structural performance is still insufficient. Additionally, there is a shortage of comprehensive studies that compile and analyze all the structural experiments conducted thus far to evaluate the GPC’s potential. Therefore, this study aimed at compiling and analyzing a number of bond, flexural, shear, and axial strength tests of GPC to assess its potential as a substitute for OPC and to identify its distinctive characteristics compared to OPC. As a result, it is considered that GPC can be used as a substitute for OPC without any structural safety issues. However, caution is needed in terms of deflection and ductility, and additional experiments are deemed necessary in the aspect of compressive strength of large-scale members.

This paper presents experimental testing results on full-scale RC column specimens subjected to quasi-static cyclic loading. Two types of lap-spliced steel rebars were used: hot-rolled thermo-mechanically treated (TMT) and cold-twisted ribbed bars. The specimens were tested under varying axial load levels: CD-10 and CD-20 specimens, reinforced with TMT bars, were loaded at 10% and 20% of the column's axial load capacity, respectively, while CT-20 specimen, reinforced with cold-twisted ribbed bars, was axially loaded at 20% capacity. In contrast to the cold-twisted bars, the TMT bars’ yield strength exceeded the specified strength by 38%, leading to an underestimation of the required rebar splice length and significantly impacting cracking patterns and curvature near the dowel end. The CD-20 and CT-20 specimens showed comparable lateral load capacity and initial stiffness, substantially higher than the CD-10 specimen. The CT-20 specimen exhibited symmetrical hysteretic behavior, indicating a consistent response to reversed cyclic loading, with (on average) 10% and 45% higher peak and ultimate displacement capacity than CD-10 and CD-20, respectively, and 45% higher displacement ductility capacity. Notably, only the CT-20 specimen met the acceptance criteria for structural testing described by the code of practice, while the lower ductility and ultimate rotation capacity of CD-10 and CD-20 resulted from the unintended increase in rebar yield strength.

Ultra-high-performance concrete (UHPC) is considered a material with high strength and good ductility. However, it was found in the experiments that the ductility of slender UHPC walls at high axial-load ratios (ALRs) was not as good as expected. The improvement on the ALR limit of the walls by using UHPC is limited. Thus, this study theoretically investigated the ALR limit of slender UHPC wall-type piers. Equivalent UHPC stress block and equivalent steel strip methods were used to calculate the bearing capacity of UHPC wall-type piers. The calculation results were in good agreement with the summarized experimental and numerical results. Based on the experimental observations and the proposed calculation method, the failure mechanism of the UHPC wall-type piers was theoretically analyzed. Equations for determining the ALR limit of UHPC wall-type piers and suggestions for designing UHPC wall-type piers were proposed. It was suggested that high-strength steel bars should be used with caution in T-section UHPC wall-type piers, especially when the reinforcement ratio is higher than 3%. This study provided references for the compilation of the Chinese Code “Technical Specification for Ultra-High-Performance Concrete Structures.”