Stiffness reduction factor for post-tensioned flat plate slabs

2층 규모의 철근콘트리트조 및 포스트텐션조 무량판구조를 1/3 스케일로 축소하여 제작한 실험체의 진동대 실험 결과를 바탕으로 무량판구조의 모델링 기법을 향상하고자 하는 연구를 수행하였다. 이 연구에서 적용한 모델링 방법은 슬래브의 휨모멘트에 의한 휨파괴, 불균형모멘트의 전달에 의한 휨파괴 및 펀칭전단파괴에 의한 슬래브-기둥 접합부의 모멘트 전달능력 상실등의 영향을 반영하는 매우 포괄적인 구조해석 방식이다. 펀칭전단파괴에 대해서는 중력비와 층간변위각에 기초한 한계상태 모델이 적용되었다. 이 논문에서 제안된 비선형 모델은 무량판구조의 진동대 실험 결과와 잘 부합하는 것으로 나타났다.

Post-tensioning has become a strong contender for manufacturing reinforced concrete (RC) members, especially for flat slabs in large-span structures. Post-tensioned (PT) slabs can lead to considerable material savings while reducing the embodied carbon (embodied CO2), construction time, and life cycle maintenance and repair costs. In this research, a novel hybrid Firefly–Artificial Neural Network (Firefly–ANN) computational intelligence model was developed to estimate the cost effectiveness and embodied CO2 of PT slabs with different design variables. To develop the dataset, several numerical models with various design variables, including the pattern of tendons, slab thickness, mechanical properties of materials, and span of slabs, were developed to investigate the sustainability and economic competitiveness of the derived designs compared to benchmark conventional RC flat slabs. Several performance measures, including punching shear and heel drop vibration induced by human activity, were used as design constraints to satisfy safety and serviceability criteria. The economic competitiveness of PT slabs was more evident in larger spans where the cost and embodied CO2 emissions decreased by 39% and 12%, respectively, in PT slabs with a 12-m span length compared to conventional RC slabs. Sensitivity analysis also confirmed that the cost and embodied CO2 emissions were very sensitive to the slab thickness by 86% and 62%, respectively.

Static pushover response of spring anchored unbonded post-tensioned rocking systems

The flat slab is gaining popularity among architects. The flat plate slab provides a way for architect to achieve completely flat ceiling with no beam protrusion. There is also improvement in the construction speed and cost savings from using this system which requires only simple formwork. But when load acting on the slab is large or clear span between columns is more so it is required to increase the slab thickness; hence the self –weight of slab is increased due to increased volume of slab and also more amount of steel is required to resist this increased weight of slab. Voided slabs eliminate concrete where it isn’t needed and the subsequent weight reduction due to this eliminated concrete makes longer span possible. In this study the design process for flat plate slab is compared with voided slab lightened with U-Boot Beton through a design comparison of total slab area 40m by 40m having panels of 10m by 10m and also the deformation of both type of slabs is analysed by using ETABS software.

ETABS software is used to analyze the structural response of reinforced concrete (RCC) and post-tensioned (PT) slabs under lateral loading. This study investigates RCC and PT slabs’ behavior by using finite element analysis to determine bending moments, shear forces, and storey drift. Prestrassed slabs display lower bending moments and shear forces than RCC slabs, demonstrating the effectiveness of prestressing in reducing structural requirements. A reduction in storey drift also indicates improved resistance to lateral deformations in PT slabs. In terms of structural performance and cost-effectiveness, PT slabs offer potential benefits for constructing layouts and construction, making them an attractive choice.

self-centering wall (SCW) is a lateral resistant rocking system that incorporates posttensioned (PT) tendons to provide a self-centering capacity along with dampers to dissipate energy. This paper investigates the rocking responses of a SCW with base viscous dampers under a sinusoidal-type pulse considering yielding and fracture behaviour of the PT tendon. The differences in the overturning acceleration caused by different initial forces in the PT tendon are computed by the theoretical method. The exact analytical solution to the linear approximate equation of motion is also provided for slender SCWs. Finally, the effects of the ductile behaviour of PT tendons on the rocking response of a SCW are analysed. The results demonstrate that SCWs exhibit two overturning modes under pulse excitation. The overturning region with Mode 1 in the PT force cases separates the safe region of the wall into two parts: region S1 with an elastic tendon and region S2 with a fractured tendon. The minimum overturning acceleration of a SCW with an elastic-brittle tendon becomes insensitive to excitation frequency as the PT force increases. After the plastic behaviour of the PT tendon is considered, the minimum overturning acceleration of a SCW is increased significantly in the whole range of the studied wg/p

Seismic behavior of self-centering prestressed precast concrete frame subassembly using steel top and seat angles

Progressive collapse mechanisms of post-tensioned reinforced concrete frames considering effect of infill walls

Forensic investigation after the failure of a bonded post-tension (PT) tendon has shown that in most cases, these failures occur because the strands were not properly protected by the grout. There is often a void or deficient grout which provides an environment that will lead to strand corrosion, and if left unmitigated, eventually failure. Identification of PT tendon grout defects is very difficult to perform with standard inspection techniques and these PT issues are commonly not identified until a serious failure occurs. This paper will review the innovative ways nondestructive testing can locate voided or defective grout and document corrosion in external and internal PT tendons. The paper will focus on the use of the acoustic method, impact echo/pulse velocity (IE/PV), which can determine voiding by analyzing the amplitude and frequency of the resonating compressional, and shear waves along the PT tendons. Through analysis of these stress waves, a trained practitioner can locate defects in the grouting of both internal and external tendons. The paper will provide case studies of two different bridges where a failed PT tendon on each structure prompted an investigation into the condition of the other tendons. It was discovered that grout voids were a prominent issue throughout the structures and that corrosion was at advanced stages.

Finite element analysis of concrete filled tube column to flat plate slab joint

The post-tensioned slabs have been using for many years. Over the years, many guidelines regarding design methods and calculations have been issued. There are several methods of static analysis and obtained results interpretation. It should be noted that the selection of method has a large impact on the final results in terms of required amount of presstresing steel. It is a great importance for economic aspects of realization of the post-tensioned slabs. In this paper the results of analysis of flat post-tensioned slab are presented. The calculations were carried out using two methods: the equivalent frame method and final elements method. The differences between these two methods and the impact of the selected method on the final usage of the prestressing steel are described in detail.

Performance-based design is the growing paradigm in contemporary structural engineering, and structural fire safety engineering is no exception. Advocates of performance-based methodologies seek to adopt sophisticated fire strategies tailored to individual building needs. In particular, these strategies are being applied to optimized reinforced concrete buildings, including post-tensioned (PT) structures. The current understanding of prestressing steel behavior based largely on outdated research that fails to properly account for material property changes at elevated temperatures. Furthermore, real fires in real PT concrete buildings have the potential to induce unique failure mechanisms that cannot be observed or accounted for using standard fire tests, as seen through case studies of real fires (see Chap. 3). Current modelling tools used to establish structural fire safety engineering strategies lack realistic experimental validation and verification, leading to the development of potentially unconservative performance-based strategies for PT concrete buildings. In order to enable credible performance based design of PT concrete buildings current modelling capabilities need to be improved, through the analysis of densely instrumented experiments, which incorporate as many relevant structural properties (post-tensioning, continuity, restraint, realistic scale, unbonded reinforcement, etc.) of as-built PT construction as possible. This need is partly addressed in the current chapter by presenting experiments on three 3-span continuous, restrained PT concrete slabs (slab strips). The slabs were put under sustained service loading and exposed to severe localized heating using radiant heaters. This chapter considers an extensive recent experimental program conducted for this book over the years 2011–2013. This experimental program compliments those discussed in previous chapters. Three novel large-scale tests on locally heated, continuous PT concrete slab strips are detailed. In real and contemporary multiple bay and continuous unbonded post tensioned (UPT) concrete slabs exposed to fire, structural actions may play significant (often inter-related) roles influencing the response of this construction. This response is studied and explained herein.

This paper proposes a new post-tensioned (PT) precast bridge column (PBC) with a socket connection. PT steel tendons and unbonded steel rebars provide self-centering capability and energy-dissipating capacity, respectively. Because the PT tendons are off-site anchored, they can effectively shorten the on-site working time and improve the safety and tolerance of construction. After describing the configuration and mechanism of the PBC, the analytical equations governing its cyclic behavior are derived. In the quasi-static cyclic loading test results, five PBC specimens and one cast-in-place (CIP) bridge column are designed, based on the criteria that their lateral “yield” strengths are identical, i.e. the concept of equivalent lateral force design. The results show that the PBC specimens realized the targeted lateral strength and exhibited self-centering damping behavior. Compared with the test data, the errors of the “yield” and ultimate strengths predicted by the analytical equations were −9.3% and 8.0%, respectively. The PBC specimens remained nearly intact throughout the tests, although minor cracks were detected in the concrete. In contrast, spalling of concrete and buckling of rebars were observed in the CIP specimen. The comparisons between the PBC specimens indicated that the novel bridge column could maintain self-centering capability and achieve the largest damping capacity when the lateral force-resisting contribution ratio of energy-dissipating steel rebars is 35%, the PT tendons are prestressed to 35% of ultimate stress with a reinforcement ratio of 0.35%, and the embedded depth is 0.7 times the width of the column.

This paper presents a numerical investigation of a post-tensioned flat slab without conventional longitudinal reinforcement; only steel fibres were employed to ensure sufficient ductility and shear capacity of the slab. Results were taken from a reported experiment conducted on a full scale steel fibre-reinforced flat slab (0.38% fibre content) which was tested until failure, undergoing a ductile bending failure. A nonlinear finite element analysis was employed to study the experiment, including the ultimate state. A parametric study was performed using the numerical model to investigate the influence of the tensile behaviour of steel fibre-reinforced concrete (SFRC) on the structural response. The model proved to be relatively sensitive to changes in the tensile behaviour, but the differences were not prominent until entering the nonlinear area of the load-displacement curve. A constant curve with tensile stress equal to the residual tensile strength of the SFRC provided a robust numerical model and results on the conservative side. Including a peak stress with a multilinear tensile curve provided a less stable analysis but more accurate results. However, the model behaviour was stiffer than the experiment, providing too small deformations at failure. Nevertheless, the numerical model was able to display the ductile bending failure mode and moment redistribution.

SummaryPrecast concrete structures are increasingly being adopted by building designers in regions of high seismicity. An unbonded posttensioned (PT) precast split shear wall system (UPPSSW) was proposed by the Precast Seismic Structural Systems (PRESSS). The UPPSSW system is composed of two or more single precast concrete wall panels that are connected together with energy‐dissipating shear connectors and anchored to the foundation with unbonded PT tendons located at the panel center. In this paper, an optimum design program has been developed for designing this system. The objective of the optimum process is to find the optimum combination between PT tendons and shear connectors while keeping the moment capacity of the wall equal to the applied design moment and achieving zero residual drift simultaneously. In addition, MATLAB was employed to explore an optimization program using genetic algorithm. Compared with the existing design methods for the system, the optimum design program proposed in this research is accurate, efficient, and direct. Moreover, it can yield the optimum design automatically and quickly. As a result, the existing lengthy and manual design process of trial and error for the system can be avoided.