Jiepeng Liu

Dynamic Performance Characteristics of Pre-Stressed Cable RC Truss Floor System under Human-Induced Loads

Excessive floor vibrations in slender structural systems due to human activity are becoming more prevalent. This may result in serviceability problems such as discomfort to occupants and even subsequent public panic. This paper describes the experimental and analytical studies on the vibration performance of a long-span pre-stressed cable RC truss (PCT) floor system, along with an extensive comparison between the present results and the current vibration design criteria used in the USA and China. The dynamic responses of this floor system under heel-drop, falling-into-seats, and jumping loads were obtained through on-site tests. The test results show good agreement in natural frequencies of the PCT floor system with others, but there are obvious differences in peak accelerations and damping ratios. A method based on the classical plate theory was adopted to determine the fundamental frequency of the system. Dynamic magnification factors (DMFs) under different loads were calculated using the inversion technique and then compared with the results available from others. Some of the conclusions achieved may be incorporated into the structural design of the system of concern to improve safety and serviceability. They can also serve as the basis for developing the relevant design guideline.

Vibration of Prestressed Cable RC Truss Floor System due to Human Activity

AbstractVibration has become a serious serviceability problem due to the large openings of girder, lightweight floor systems, and high-strength materials used in practice. The results from both heel-drop and jumping floor vibration tests of a large-span prestressed cable RC truss (PCT) floor system are presented. System parameters such as peak acceleration, fundamental frequency, and damping ratios were considered and studied. The results and comparisons were taken based on the on-site test data. The comparison results indicate inconsistencies with the heel-drop or jumping impact models proposed by other researchers. The results from heel-drop and jumping tests were comprehensively compared against published codes. Based on the classic plate theory, a derived accurate formula for a PCT floor system is proposed. Lastly, a simplified method is suggested, which uses the constant moment of inertia for the cross section of a PCT girder.

Vibration serviceability of pre-stressed concrete floor system under human activity

Abstract A comprehensive research was undertaken to study the vibration serviceability of a long-span pre-stressed concrete floor system intended to be used in an indoor badminton court, using the field test and finite element method. Specifically, heel-drop was adopted to capture the natural frequencies and modal damping ratios of the floor system and the tests for jumping impact and different types of human excitations (walking, running and hopping) were performed to capture the acceleration responses. The floor system is found to have low frequency and modal damping ratio. The comparison of the experimental results with the published values from China’s design code, AISC design guide and PCI design handbook indicates that the pre-stressed concrete floor system exhibits satisfactory vibration perceptibility overall. The acceleration threshold value given in the China’s code and AISC design guide may be conservative for the pre-stressed concrete floor under hopping excitation. For determining the fundamental natural frequency analytically, fixed-pinned support condition is recommended for accounting for the effect of adjacent structures on floor stiffness. Coefficients βrp is proposed to calculate the RMS acceleration conveniently by hand.

Effect of friction on axially loaded stub circular tubed columns

This article discusses the influence of bond and friction between the steel tube and concrete on composite response for circular tubed-reinforced-concrete short columns under axial compression. Thirteen large diameter-to-thickness ratio (D/t = 133,160) circular tubed stub columns with different types of the steel tubes (galvanized or not) and five reinforced concrete counterparts were tested. Although circular tubed–reinforced concrete specimens were characterized by the shear failure mode, the ductility performance was much better than the reinforced concrete specimens. A simplified theoretical model and a three-dimensional finite element analysis model were developed to analyze the bond and friction behavior of circular tubed-reinforced-concrete columns. The stress state of the steel tubes is determined by the friction coefficient because slipping occurred between the tube and its in-filled concrete. The formulas considering friction coefficient are also proposed for the prediction of the axial loading resistances of circular tubed concrete stub columns. The predicted results are in good agreement with the experiment results and nonlinear finite element analysis results.

Behavior and Strength of Circular Tubed Steel- Reinforced-Concrete Short Columns under Eccentric Loading

This paper presents the results of experimental studies on circular tubed steel-reinforced-concrete (TSRC) short columns subjected to axial and eccentric loading. A total of 12 columns with the key parameters of eccentricity ratio and diameter-to-thickness ratio of the steel tube were tested. The effect of shear studs on the co-work behavior of concrete and shaped steel was studied. The test results indicated that the shear studs affected little on the failure mode, bearing capacity and ductility of the eccentrically loaded circular TSRC short columns. Elastic-plastic analysis for the steel tube showed that the tubes at the compression side began to yield when the load approximately reached 90% of the peak load. Fiber-based numerical models for circular TSRC short columns were established and the results accorded well with the experimental results. Furthermore, the whole section plastic assumption in EC4 was adopted to determine the section capacity interaction diagram for circular TSRC columns.

Vibration Behavior of Prestressed Cable Reinforced Concrete Truss System Caused by Jumping and Hopping

AbstractJumping and hopping are considered the most severe human loading scenario for stadiums and gymnasiums. Recent design methods examine floor vibration by requiring knowledge of the dynamic ch...

Experimental and analytical studies on the vibration serviceability of long-span prestressed concrete floor

An extensive experimental and theoretical research study was undertaken to study the vibration serviceability of a long-span prestressed concrete floor system to be used in the lounge of a major airport. Specifically, jumping impact tests were carried out to obtain the floor’s modal parameters, followed by an analysis of the distribution of peak accelerations. Running tests were also performed to capture the acceleration responses. The prestressed concrete floor was found to have a low fundamental natural frequency (≈ 8.86 Hz) corresponding to the average modal damping ratio of ≈ 2.17%. A coefficients βrp is proposed for convenient calculation of the maximum root-mean-square acceleration for running. In the theoretical analysis, the prestressed concrete floor under running excitation is treated as a two-span continuous anisotropic rectangular plate with simply-supported edges. The calculated analytical results (natural frequencies and root-mean-square acceleration) agree well with the experimental ones. The analytical approach is thus validated.

Cyclic shear behavior and shear strength of steel tubed-reinforced-concrete short columns

The steel jacketing approach is effective and economic for retrofitting reinforced concrete short column. Steel jacketed concrete columns are referred as steel tubed-reinforced-concrete columns when applying in new building structures. To investigate the cyclic shear behavior and shear strength of tubed-reinforced-concrete short columns with a large diameter-to-thickness/width-to-thickness ratio (D/t), four specimens were designed and tested under a constant axial compression combined with quasi-static cyclic lateral loading. Three main system parameters were considered in the test: (1) type of column cross section (circular and square), (2) D/t (106–150), and (3) axial load ratio (0.4 and 0.6). All the columns showed shear-failure mode during the tests, and the sheared plates of steel tubes yielded when the peak load had reached. The circular columns showed good ductility, while the square ones were just in opposite. Based on the analysis results, a simplified shear strength model for both circular and square columns is proposed, in which the relationship between cyclic shear strength and lateral drift ratio of the columns and the shear-resisting mechanisms for both shear and hoop stresses of the tube are considered.

Research on mechanical behavior ofL-shaped multi-cell concrete-filled steel tubular stub columns under axial compression

A total of 11 L-shaped multi-cell concrete-filled steel tubular stub columns were fabricated and researched in axial compression test. The key factors of width-to-thickness ratio D/t of steel plates in column limb and prism compressive strength of concrete fck were investigated to obtain influence on failure mode, bearing capacity, and ductility of the specimens. The test results show that the constraint effect for concrete provided by multi-cell steel tube cannot be ignored. The ductility decreases with the increase of width-to-thickness ratio D/t of steel plates in column limb. The bearing capacity increases and the ductility decreases with the increase in prism compressive strength of concrete fck. A finite element program to calculate concentric load–displacement curves of L-shaped multi-cell concrete-filled steel tubular stub columns was proposed and verified by the test results. A parametric analysis with the finite element program was carried out to study the influence of the steel ratio α, steel yield strength fy, prism compressive strength of concrete fck, and width-to-thickness ratio D/t of steel plates in column limb on the stiffness, bearing capacity and ductility. Furthermore, the design method of bearing capacity was determined based on mainstream concrete-filled steel tubular codes.

Numerical analysis on seismic behaviors of T-shaped concrete-filled steel tubular columns with reinforcement stiffeners

A numerical analysis based on previous experiment has been carried out on T-shaped concrete-filled steel tubular columns subjected to constant axial compressive load and cyclic lateral loads. Tensile bar stiffeners were introduced to be welded on inside surfaces of steel tube to postpone its local buckling and to enhance the confinement of steel tube for concrete. A modified fiber-based method was developed to establish numerical modeling program of specimens’ cyclic behavior, incorporating the effect of stiffeners on postponing steel tube’s local buckling and the confinement for concrete. The reciprocating movement of inflection point along frame column is also considered in the numerical program. A simplified arc-length method was employed as iterative control algorithm of the numerical model. Horizontal load–displacement hysteretic curves of specimens were calculated with the numerical model and verified with test results. A restoring force model based on experimental investigation was proposed as simplified method for engineering practice.