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CONTENTS
Volume 37, Number 4, November25 2020
 

Abstract
Human-induced vibration could present a serious serviceability problem for large-span and/or lightweight floors using the high-strength material. This paper presents the results of heel-drop, jumping, and walking tests on a large-span composite steel rebar truss-reinforced concrete (CSBTRC) floor. The effects of human activities on the floor vibration behavior were investigated considering the parameters of peak acceleration, root-mean-square acceleration, maximum transient vibration value (MTVV), fundamental frequency, and damping ratio. The measured field test data were validated with the finite element and theoretical analysis results. A comprehensive comparison between the test results and current design codes was carried out. Based on the classical plate theory, a rational and simplified formula for determining the fundamental frequency for the CSBTRC floor is derived. Secondly, appropriate coefficients (Brp) correlating the MTVV with peak acceleration are suggested for heel-drop, jumping, and walking excitations. Lastly, the linear oscillator model (LOM) is adopted to establish the governing equations for the human-structure interaction (HSI). The dynamic characteristics of the LOM (sprung mass, equivalent stiffness, and equivalent damping ratio) are determined by comparing the theoretical and experimental acceleration responses. The HSI effect will increase the acceleration response.

Key Words
vibration serviceability; composite steel bar truss-reinforced concrete (CSBTRC) floor; human-structure interaction; large-span floor; fundamental frequency

Address
Liang Cao, Jiang Li and Xing Zheng: School of Civil Engineering, Chongqing University, Chongqing 400045, China;
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University),
Ministry of Education, Chongqing 400045, China
Y. Frank Chen: Department of Civil Engineering, The Pennsylvania State University, Middletown, PA 17055, USA


Abstract
The application of double-skin composite wall should meet different layout plans. However, most available research focused on the rectangular section with uniform axial compression. In this research, the structural behavior of double-skin composite wall with L section was studied. Due to the unsymmetric geometric characteristics, the considered loading condition combined the axial compression and biaxial bending. Five specimens were designed and tested under eccentric compression. The variables in the test included the width of the web wall, the truss spacing, the thickness of the steel faceplate, and the thickness of the web wall. The test results were discussed in terms of the load-displacement responses, buckling behavior, stiffness, ductility, strength utilization, strain distribution. Two modern codes were employed to predict the interaction between the axial compression and the biaxial bending. The method to calculate the available bending moment along the two directions was proposed. It was found that CECS 159:2004 offers more suitable results than AISC 360.

Key Words
composite wall; eccentric compressive loading; experimental behavior; T-shaped section; truss connector

Address
Ying Qin: Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing, China;
School of Civil Engineering, Southeast University, Nanjing, China
Xin Chen, Wang Xi, Xingyu Zhu and Yuanze Chen: School of Civil Engineering, Southeast University, Nanjing, China


Abstract
Composite structures are generally pressurized at both sides when repaired by the scarf repair method. But single-face vacuum bag curing (SVC) may be used in some practical scarf repair of penetration damage due to the low accessibility of composite structures, which can decrease bonding quality and may reduce structural mechanical properties. In this paper, experimental investigations were conducted on tensile and compressive properties of scarf-repaired composite laminates using SVC and double-face vacuum bag curing (DVC) in four hygrothermal environments. Finite element models of composite scarf joints with voids were established to further explore the failure mechanism of scarf-repaired laminates. Results show that the curing condition hardly affects tensile and compressive properties of the repaired laminates though it significantly affects the bonding quality with adhesive inner voids. Failure loads of scarf joints almost keep unchanged with adhesive voids increasing.

Key Words
scarf-repaired composite laminate; curing condition; static mechanical properties; hygrothermal effect

Address
Xiaoquan Cheng, Yujia Cheng and Xin Guo: School of Aeronautic Science and Engineering, Beihang University, Beijing, 100083, China
Jie Zhang: Institute of Telecommunication and Navigation Satellites, China academy of spacecraft technology, Beijing, 100094, China
Wenjun Huang: AVIC China Helicopter Research and Development Institute, Jingdezhen 333001, China

Abstract
This paper presents the flexural performance of double skin composite beams (DSCBs) at different Arctic low temperatures. 12 DSCBs were prepared and tested under two-point loading at different Arctic low temperatures of 20, -30, -50, and -70C. The studied parameters include low-temperature level (T), steel-faceplate thickness (t), shear span ratio (), and spacing of headed studs (S). The experimental investigations under two-point loading tests showed that flexural failure occurred to all DSCBs, even including the specimen designed with the small ratio of 2.9. The ultimate strength behaviours of DSCBs were improved due to the improved mechanical properties of constructional materials and the confinement on shear connectors. The DSCB subjected to two-point loading and low temperatures exhibits a five-stage working mechanism. The stiffness and strength indexes of DSCBs increase linearly with temperature and t value increasing, while decreasing as shear span ratio boosts. In the contrast, the change of S value from 150 to 200 mm has little effect on the ultimate strength behavior of DSCB.

Key Words
double skin composite structure; composite structure; low temperature; flexural behaviour; bending tests; Arctic structures

Address
Jia-Bao Yan and Xin Dong: School of Civil Engineering / Key Laboratory of Coast Civil Structure Safety of Ministry of Education,
Tianjin University, Tianjin 300350, China
Tao Wang: Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics,
CEA, Harbin 150080, China



Abstract
In this paper, a simplified seismic design method for low-rise dual frame-steel plate shear wall (SPSW) structures is proposed in the framework of performance-based seismic design. The dynamic response of a low-rise structure is mainly dominated by the first-mode and the structural system can be simplified to an equivalent single degree-of-freedom (SDOF) oscillator. The dual frame-SPSW structure was decomposed into a frame system and a SPSW system and they were simplified to an equivalent F-SDOF (SDOF for frame) oscillator and an equivalent S-SDOF (SDOF for SPSW) oscillator, respectively. The analytical models of F-SDOF and S-SDOF oscillators were constructed based on the OpenSees platform. The equivalent SDOF oscillator (D-SDOF, dual SDOF) for the frame-SPSW system was developed by combining the F-SDOF and S-SDOF oscillators in parallel. By employing the lateral force resistance coefficients and seismic demands of D-SDOF oscillator, the design approach of SPSW systems was developed. A 7-story frame-SPSW system was adopted to verify the feasibility and demonstrate the design process of the simplified method. The results also show the seismic demands derived by the equivalent dual SDOF oscillator have a good consistence with that by the frame-SPSW structure.

Key Words
steel plate shear wall; SDOF oscillator; dual structural system; performance-based seismic design; seismic demand

Address
Jiulin Bai and Jianyuan Zhang: School of Civil Engineering, Chongqing University, Chongqing, 400045, China;
Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University),
Ministry of Education, Chongqing 400045, China
Ke Du: Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics,
China Earthquake Administration, Harbin 150080, China
Shuangshuang Jin: School of Civil Engineering, Chongqing Jiaotong University, 400074, Chongqing, China



Abstract
Currently, there are many lateral resisting systems utilized in resisting lateral loads being produced in an earthquake. Such systems can significantly reduce the roof's displacement when placed at an optimum location. Since in the design of tall buildings, the minimum distance between adjacent buildings is important. In this paper, the critical excitation method is used to determine the best location of the belt truss system while calculating the minimum required distance between two adjacent buildings. For this purpose, the belt truss system is placed at a specific story. Then the critical earthquakes are computed so that the considered constraints are satisfied, and the value of roof displacement is maximized. This procedure is repeated for all stories; i.e., for each, a critical acceleration is computed. From this set of computed roof displacement values, the story with the least displacement is selected as the best location for the belt truss system. Numerical studies demonstrate that absolute roof displacements induced through critical accelerations range between 5.36 to 1.95 times of the San Fernando earthquake for the first example and 7.67 to 1.22 times of the San Fernando earthquake for the second example. This method can also be used to determine the minimum required distance between two adjacent buildings to eliminate the pounding effects. For this purpose, this value is computed based on different standard codes and compared with the results of the critical excitation method to show the ability of the proposed method.

Key Words
critical excitation method; minimum required distance; linear dynamic analysis; time history analysis

Address
Reza Kamgar: Department of Civil Engineering, Shahrekord University, Shahrekord, Iran
Peyman Rahgozar: College of Design, Construction and Planning, University of Florida, Gainesville, Florida, USA


Abstract
Twenty-two corrosion-damaged columns were simulated through accelerated steel corrosion tests. Eight specimens were directly tested to failure under axial load, and the remaining specimens were tested after concrete-filled steel tube (CFST) strengthening. This study aimed to investigate the damage of RC columns after corrosion and their restoration and enhancement after strengthening. The research parameters included different corrosion degrees of RC columns, diameter-to-thickness ratio of steel tube and the strengthening concrete strength. Experimental results showed that CFST strengthening method could change the failure mode of corrosion-damaged RC columns from brittleness to ductility. In addition to the bearing capacity provided by the strengthening materials, it can also provide an extra 26.7% amplification because of the effective confinement provided by steel tubes. The influence of corrosion on reinforcement and concrete was quantitatively analysed and considered in the design formula. The proposed formula accurately predicted the bearing capacity of the strengthened columns with a maximum error of only 7.68%.

Key Words
corrosion-damaged; RC column; CFST; strengthening; axial compression

Address
Hongjun Liang, Yanju Jiang, Yiyan Lu and Jiyue Hu: School of Civil Engineering, Wuhan University, Wuhan 430072, China

Abstract
The paper describes an optimization method based on the mathematical model of interaction within multibody 'bridge-track-cars" dynamic system. The interaction is connected with considerable dynamic phenomena influenced by high traffic speed (up to 400 km/h) on high-speed railroads. The trend analysis of a structure is necessary to determine the direction and resource of optimizing the system. Thus, scientific methods of decision-making process are necessary. The process requires a great amount of information analysis dealing with behavior and changes of the "bridge-track-cars system" that consists of mechanisms and structures, including transitions. The paper shows the algorithm of multi-criteria optimization that can essentially reduce weight of a bridge superstructure using big data analysis. This reduction is carried out in accordance with the constraints that have to be satisfied in any case. Optimization of real steel-concrete beam is exemplified. It demonstrates possibility of measures that are offered by the algorithm.

Key Words
high-speed railroads; bridges; composite structures; multibody dynamics; optimal design

Address
Vladimir Y. Poliakov: Bridges and Tunnels Department, Russian University of Transport, Moscow, Russia
9b9, Obrazcova Street, Moscow Russia
Vasyli V. Saurin: Institute of Problems of Mechanics, Russian Academy of Sciences, 101, Pr. Vernadskogo, Moscow, Russia



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