Vol.37/No.1(143)(2022)
| Title | Bond Splitting Performance of Concrete and Development Length in Tension for High-Strength Deformed Bars |
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| Author | Ker-Chun Lin, Yuan-Yan Lin, Kai-Ning Chi, Sheng-Jhih Jhuang, Yung-Chih Wang |
| Keywords | High-strength reinforced concrete, development length, modification factor of steel grade, split index, bond stress |
| Abstract | For ACI 318-19 Code, a modification factor of steel grade of Ψ that is equal to 1.15 or 1.3 for 550 or 690 MPa grade of steel bar exceeding 420 MPa was added to increase straight development length in tension for deformed bar. It is known that the design equation of development length stipulated in the existing ACI 318 Code was obtained based on a mechanism of concrete splitting primarily dominated by contact characteristics between concrete and steel bar. This paper was intended to investigate the rationality of the Ψ included in the design equation of development length. A total of 20 beam-end specimens was carried out to study bond behaviors of concrete splitting with a deformed bar in this research. A #10 bars for three various grades of 420, 550 and 690 MPa was used as developed steel bar per specimen. Concrete strength and split index were study parameters as well. Test results indicated that the anticipated concrete splitting occurred in 15 specimens of all 20 ones even took place in the specimens with the split index of 4.93. Based on analysis overcomes of the test bond stress in this research, it was confirmed that under upper limitations of 70 MPa for the concrete strength and 2.5 for the split index, the average bond stresses of the three various grade bars for ACI 318-14 Code ranged from 1.72 to 2.4. The modification factor of steel grade of Ψ seemed to not be needed in the provisions of straight development length of ACI 318-19 Code. It was certificated as well that raising the limit limitations of 100 MPa for the concrete strength and 5.0 for the split index, good results with around 10% conservative margin could be obtained according to the provisions of straight development length of ACI 318-14 Code. However, a safety factor should be considered for applications of engineering practice. |
| Title | Establishment of Time Dependent Functions for Ordinary and Pozzolanic Concrete Compressive Strength and Modulus of Elasticity in Taiwan |
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| Author | Ying-Chieh Wang, Wen-Cheng Liao |
| Keywords | fly ash, slag, strength, elastic modulus, time function |
| Abstract | Concrete is a widely used construction material composed of aggregate, cement, water, mineral admixture in a specific proportion. Not only safety, longterm serviceability is also the main consideration for buildings and infrastructures made of concrete. The volume of concrete changes over time, such as shrinkage and creep, and all the above influence the long-term serviceability. The elastic modulus of concrete, mainly determined by composition of concrete, directly affects shrinkage and creep behaviors of concrete. However, because materials vary from different resources, a localized prediction model is essential to account for characteristics of concrete in Taiwan and this specific prediction model shall involve localized time function of strength and elastic modulus as well. In view of the importance of elastic modulus and strength in practical applications, and in recent years, the addition of fly ash and water-quenched blast furnace slag in concrete has been widely used, so this research also investigates the shrinkage and creep test data from the database. A comprehensive experimental program, including compression and elastic modulus tests for seven different water-to-cement ratios of ordinary concrete and six different fly ash and slag replacement ratios of water-to-binder ratio of 0.42 for 3, 7, 14, 28, 56, 91 and 180 days, were conducted. The prediction models of time function for strength and elastic modulus for ordinary and fly ash/slag concrete in Taiwan are proposed for further modification of shrinkage and creep model and practical applications. |
| Title | Brief Introduction to Applications of Second-order Analysis in Design of Steel Structures |
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| Author | Jui-Lin Peng, Liang-Jenq Leu, Siu-Lai Chan, Yao-peng Liu, Wai-Fah Chen |
| Keywords | Critical load, Direct analysis method, Notional lateral force, Initial imperfection, Second-order analysis |
| Abstract | In recent years, the steel structural design codes of advanced countries such as Europe and the United States have stipulated the related regulations of“second-order analysis” or “direct analysis method.” In fact, the second-order analysis, widely adopted in the steel structural design codes of the European Union and the Commonwealth of Nations, is the geometric nonlinear analysis. The American engineering community believes that the terms of “the secon-dorder analysis” and “the second-order bending moment” are easily confused, so the “direct analysis method” is used to replace the “second-order analysis” in the steel structural design code. Traditional steel structural design is mostly carried out on the basis of component strength, which is an indirect design concept. The second-order analysis is designed based on the strength and the stability of the overall structural system. It is a direct and more reasonable design method, which is the reason for the adoption of steel structural design codes in advanced countries such as Europe and the United States. The second-order analysis is especially suitable for the design of steel structures that combine nonhorizontal beams and non-vertical columns, have irregular shapes and aesthetic appearances, and is difficult to determine the effective length. This paper makes a preliminary introduction to the second-order analysis of steel structural design codes in advanced countries such as Europe and the United States. In order to make it easier for engineers to grasp the content, the paper especially makes key excerptions from chapters related to the second-order analysis and the direct analysis method in the steel structural design codes of various countries. It is hoped that through the introduction of this paper, domestic engineers can understand the development of steel structural design in advanced countries, and their designs can be synchronized with international designs in the future. |
| Title | Design of partial rigid joint of precast girder and beam |
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| Author | Tzu-Liang Wu, Shyh-Jiann Hwang |
| Keywords | precast, partial rigid joint, shear transfer |
| Abstract | In 2016, the Chinese Institute of Civil and Hydraulic Engineering and the Taiwan Concrete Institute began to revise the design provisions of Chapter 9 of the ” Design Code of Concrete Structures [2] “, “Precast concrete Structures”, which were approved and published by the Construction and Planning Agency Ministry of the Interior in August 2017 [3]. The revised provision is only a principle description, which is not easy for designers to understand; this article mainly provides supplementary explanations on partial rigid joint design of the code, including the description of the main content of the revised provisions, the establishment of the structural model of the precast beams, and the definition of partial rigid joint and design, and reinforcement details, etc. In particular, the path and calculation formula for possible failure of the shear force transmitted by the partial rigid join between girder and beam are proposed for the designer’s reference. Finally, a design case is provided as an illustration, so that those interested in precast design can fully understand. |
| Title | Lateral displacement and axial force protocols of the first-story steel column in buckling-restrained braced frames under near-fault earthquake motions |
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| Author | Yu-Fang Liu, Chung-Che Chou, Guan-Ru Peng, Kuan-Ju Chen |
| Keywords | static cyclic loading, loading protocol, near-fault earthquakes, nonlinear dynamic analysis, buckling-restrained brace |
| Abstract | Most of the domestic researchers considered the loading protocol for beam to column moment connections in moment resisting frame (MRF), specified by AISC, as the reference for static cyclic test. The loading protocols for buckling restrained braced frame (BRBF) had not been developed yet. The nonlinear behavior of a structure cannot be truly reflected using the loading protocols of different type of structure. Since the first story columns are generally used to represent the seismic behavior of a building, loading protocols for the first story columns in BRBF with varied axial force and lateral drift should be developed. Moreover, the loading protocols suggested by American specifications might omit the effect of near-fault earthquakes which is common in Taiwan. Therefore, the near-fault effect on buildings is necessary to be considered for better developing the loading protocols for BRBF in Taiwan. This research has completed the nonlinear static and nonlinear dynamic analysis of BRBF which is designed with various periods for a better understanding of seismic performances of BRBF and developing loading protocols for the first story columns in BRBF with varied axial force and lateral drift. The developed loading protocols for BRBF is expected to be a beneficial reference to steel structure study in the future. |