Flat Plate Structures Research Articles

Thermal Properties of Solar Collector Comprising Oscillating Heat Pipe in a Flat-Plate Structure and Water Heating System in Low-Temperature Conditions

Solar collectors are very important to the photothermal utilization of solar energy in low-temperature conditions. In this paper, a solar collector comprising an oscillating heat pipe in a flat-plate structure is designed and studied experimentally. The thermal properties are studied in detail, and we finally obtain the startup temperature and the expression of the instantaneous efficiency with a relative error of 5%. The results show that the impact of inclination angles on the startup properties of the solar collector is significant to the thermal properties. The comparisons of the efficiency of the present design and similar products are also displayed and discussed, showing that an oscillating heat pipe collector in a flat-plate structure overcomes the low efficiency, high startup temperature and bad pressure resistance of conventional solar collectors. In addition, the thermal properties of the water heating system based on the novel collector were also tested, illustrating the differences between the solar irradiance and the water heating system. Some improvements (e.g., shell material and assembly method) were made in this system design process to increase the heat transfer efficiency and solve the corrosion and pressure resistance problems.

Numerical Investigation of the Punching Resistance of Reinforced Concrete Flat Plates

AbstractNonlinear finite-element analyses are used to numerically investigate the punching shear resistance of reinforced concrete flat plate structures. Material nonlinearity is based principally ...

Load Transfer and Collapse Resistance of RC Flat Plates under Interior Column Removal Scenario

AbstractReinforced concrete (RC) flat-plate structures are vulnerable to punching shear failure at their slab-column connections, potentially leading to a catastrophic progressive collapse. In prac...

Unified equivalent frame method for post-tensioned flat plate slab structures

The post-tensioned (PT) flat plate slab system is commonly used in practice, and this simple and fast construction method is also considered to be a very efficient method because it can provide excellent deflection and crack control performance under a service load condition and consequently can be advantageous when applying to long-span structures. However, a detailed design guideline for evaluating the lateral behavior of the PT flat plate slab system is not available in current design codes. Thus, typical design methods used for conventional reinforced concrete (RC) flat plate slab structures have inevitably been adopted in practice for the lateral load design of PT flat plate structures. In the authors\' previous studies, the unified equivalent frame method (UEFM) was proposed, which considers the combined effect of gravity and lateral loads for the lateral behavior analysis of RC flat plate slab structures. The aim of this study is to extend the concept of the UEFM to the lateral analysis of PT flat plate slab structures. In addition, the stiffness reduction factors of torsional members on interior and exterior equivalent frames were newly introduced considering the effect of post-tensioning. Test results of various PT flat plate slab-column connection specimens were collected from literature, and compared to the analysis results estimated by the extended UEFM.

Numerical study on effect of integrity reinforcement on punching shear of flat plate

Reinforced concrete flat plates consist of slabs supported directly on columns. The absence of beams makes these systems attractive due to advantages such as economical formwork, shorter construction time, less total building height with more clear space and architectural flexibility. Punching shear failure is usually the governing failure mode of flat plate structures. Punching failure is brittle in nature which induces more vulnerability to this type of structure. To analyze the flat plate behavior under punching shear, twelve finite element models of flat plate on a column with different parameters have been developed and verified with experimental results. The maximum range of variation of punching stress, obtained numerically, is within 10% of the experimental results. Additional finite element models have been developed to analyze the influence of integrity reinforcement, clear cover and column reinforcement. Variation of clear cover influences the punching capacity of flat plate. Proposed finite element model can be a substitute to mechanical model to understand the influence of clear cover. Variation of slab thickness along with column reinforcement has noteworthy impact on punching capacity. From the study it has been noted that integrity reinforcement can increase the punching capacity as much as 19 percent in terms of force and 101 percent in terms of deformation.

Time-Domain Solution for Corner Diffraction of UWB Signals by Flat Plate Structures with the Higher Order Diffraction Included

ABSTRACTIn this paper, a new time-domain (TD) solution is proposed for corner diffraction by finite-edge flat plate structures. First, TD solution is considered for corner amplitude diffraction by edges of a flat plate, and then for corner slope diffraction (CSD) which takes into account the finiteness of the plate edges. To show the significance of CSD, results have been shown for diffraction of ultra-wideband signals by edges of a horn antenna which is a structure made by interconnected flat plates. The comparison between the TD solution and the numerical inverse fast Fourier transform of the corresponding frequency-domain solution validates the proposed solution. Finally, the computation times of both methods have been compared.

Analysis of Three Different Sheet-and-Tube Water-Based Flat-Plate PVT Collectors

AbstractHybrid photovoltaic and thermal (PVT) collectors with sheet-and-tube water-based flat-plate structure (simplified as STWF-PVT) are very popular because of their simple structure and ease of...

확률론적 분석방법을 이용한 공동주택의 전과정 내재 탄소배출량 분석

The purpose of this study is to analyse life cycle embodied carbon emission of apartment buildings using probabilistic analysis method as a part of research for reduction strategy of building embodied carbon emission. To that end, the structures of apartment buildings were divided into wall structure, rigid frame structure, and flat plate structure, and major building materials in terms of carbon emissions were derived. The life cycle scenario including production stage, construction stage, maintenance step, and disposal stage of the major building materials was established for evaluating the life cycle embodied carbon emission of apartment buildings. Also, 443 residential building of 38 apartment buildings constructed in last 10 years are set as the sample of this study, then major factors are derived through the correlation analysis on the features of buildings and major building materials. Probability distribution on major building materials are constructed through a goodness of fit analysis by utilizing an amount information of major factors and major building materials. The probabilistic life cycle embodied carbon emission were analyzed by structure and plan type of apartment buildings using Monte Carlo Simulation.

Effects of In-Plane Restraint on Progression of Collapse in Flat-Plate Structures

AbstractThis paper presents experimental and numerical studies of reinforced concrete flat-plate structures. Experiments were performed on six interior slab-column connections without structural in...

Numerical investigation on the heat transfer enhancement of a latent heat thermal energy storage system with bundled tube structures

The heat transfer enhancement of a latent heat thermal energy storage system with bundled tube structures using air as the heat transfer fluid (HTF) is investigated numerically. Transient simulations of the charging processes are performed based on a two-dimensional numerical model, and the melting processes of the storage units with staggered tube bundle structure and parallel tube bundle structure are compared with that of flat plate structure. The effects of the air mass flow rate and the internal fin arrangement in the staggered tube bundle storage unit are also investigated. The results show that the heat charging rate of the latent heat storage using air as the HTF can be enhanced by increasing the heat transfer surface, the degree of air turbulence and the gas flow rate; and the storage unit with staggered tube bundle structure is a good choice for its larger heat transfer surface and higher degree of air turbulence. It is also found that the internal fin arrangement has some influences on the PCM melting process, and adding internal outside-in fins that are connected to the tube inner wall can effectively enhance the PCM melting.

Behaviors of Repaired Edge Column Slab Connections after Punching Failure Using Normal and Non-Shrinkable (CAH) Concrete

Column slab connections in flat plate structures are critical part of the structure. Punching shear damage to the connections may occur during construction or post moderate earthquakes. To avoid demolishing overall structures with such damage, connections may be repaired to restore the original strength of the structures. This paper presents behavior of repaired edge column slab connections using normal concrete and non-shrinkable (CAH) concrete. Four edge connections of flat plate structure after failure were repaired using normal and non-shrinkable (CAH) concrete respectively for two connections. The connections were re-tested to fail under combined shear and moment. The results show that bonding agent Sika Top Armatec 110 Epocem gave an excellent bond between the old concrete and the repaired concrete in the tests of repaired edge column slab connection as there are no cracks observed along the concrete interface. The edge connections repaired using normal concrete can have similar strength and stiffness as the original connections when good curing is provided The edge connections repaired using an expansive CAH concrete exhibited less strength and stiffness compared to the original edge connections due to lack of surface confinement. The Superplasticizer used in CAH concrete (Mix. B) improves concrete expansion but reduce the strength of the repaired connections

Flexurally-triggered punching shear failure of reinforced concrete slab–column connections reinforced with headed shear studs arranged in orthogonal and radial layouts

Shear strength of reinforced concrete slab–column connections can be increased through the use of headed shear studs. To reduce interference with slab flexural reinforcement, stud rails are often placed in an orthogonal layout. In this layout, no stud rail is placed in regions extending from the corners of a column, as opposed to stud placement in a radial layout. Some experiments have found the absence of radial stud rails could lead to premature shear failure at slab–column connections. This problem may not have been noticeable in experiments that tested slabs with either short-spans or with a high flexural reinforcement ratio. This paper presents an experimental study to evaluate the effectiveness of these stud layouts in slab–column connections whose slabs have relatively low flexural reinforcement ratios. Three full-scale slab–column connections that represent a flat plate structure with 25ft (7620mm) spans were tested. All three specimens had an identical flexural design, in which the reinforcement ratio was 0.8%. One specimen was built without shear reinforcement, and the remaining two specimens were reinforced with shear studs in either a radial or orthogonal layout. For the specimens with shear studs, calculated shear strengths were higher than their estimated flexural strengths.

Shaking table tests of a reinforced concrete waffle–flat plate structure designed following modern codes: seismic performance and damage evaluation

SummaryShaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period PR. The test structure performed well for the simulations associated with PR = 95, 475 and 975 years but collapsed under the maximum considered earthquake of PR = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate‐to‐column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental base shear vs. top displacement relationship allowed us to compute the overstrength (1.4). It is close to the maximum established by European code EN 1998‐1 (1.5). Based on a detailed study of the test results, potential updates to current codes and design recommendations are suggested. Copyright © 2015 John Wiley & Sons, Ltd.

Dynamic hydrophobicity of heterogeneous pillared surfaces at the nano-scale

In this study, the static and dynamic behaviors of nano-scale water droplets on heterogeneous surfaces were investigated using molecular dynamics simulations. The surface consisted of a flat plate and pillar structures. The surface was designed with four pillar heights and three pillar characteristic energies. Simulations were first run so that the water droplet reached the static equilibrium state. Once the static water droplets were in Cassie-Baxter state, increasing the pillar height had very little effect on the contact angle. Droplets on the surface with the strongest pillar characteristic energy never reached the Cassie-Baxter state and contact angles tended to decrease with increasing pillar height. Then five forces were applied to the water droplets parallel to the surface to observe the dynamic behavior of the droplets. Then, the effect of the pillar characteristic energy on the behavior of the dynamic water droplet was discussed using the contact angle hysteresis (cosθ Re − cosθ Ad) as the pillar height and the magnitude of the applied force varied. When compared to the homogeneous cases, it was found that except at the lowest pillar height all of the lower pillar characteristic energy cases were hydrophobic and did not depend much on pillar height or magnitude of force. Whereas the higher pillar characteristic energy cases were generally hydrophilic and the hydrophobicity depended greatly on the magnitude of the force.

Resistance of Flat-Plate Buildings against Progressive Collapse. I: Modeling of Slab-Column Connections

AbstractA macromodel for slab-column connections is created for use in the system-level progressive collapse analyses of reinforced concrete flat-plate structures. The proposed model jointly uses shell and connector elements to simulate the complex behavior of slabs. Shell elements are used to simulate the flexural response of slab and the load redistribution over floor slabs. The connector elements, which permit simulating separation of slab from column on a punching failure, are defined with nonlinear responses for primary bending moment and torsion. A deformation-based punching failure criterion is defined for connector elements to simulate the punching failure at a slab-column connection and failure propagation. Parameters defining concrete tension stiffening behavior under static loading, including the peak tensile stress and the tensile strain when stress degrades to zero, are calibrated from two experiments. To ensure applicability, the proposed model is validated by 24 large-scale tests conducted ...

Nonlinear model simulating load–deformation relationship of flat plate structures

In this study, an analytical method for flat plate systems subjected to lateral load was developed for application to nonlinear static analysis. In the case of flat plate systems, it has been recognized that the structural damages developed by gravity and lateral load are concentrated at their slab–column connections. To investigate such behavioral characteristics of the connections, three independent nonlinear hinges were introduced with simulating flexural, shear, and torsional nonlinearity. The behavior of the nonlinear hinges was defined by using backbone curves based on current design codes of KCI 2012 and ACI 318-11. The columns and slabs, excluding the slab–column connections, were modeled by elastic line and plate elements. For verification, the proposed analytical method was applied to existing test specimens subjected to unbalanced moment. The analysis results showed that the proposed method can simulate the entire load–deformation behavior of the test specimens, including the strength and deformation capacity. In addition, parametric studies were performed with respect to primary test parameters: column aspect ratio, gravity load ratio, effective depth, reinforcement ratio, slab length, and boundary condition. The effect of these primary test parameters on the structural behavior of the flat plate systems was also investigated.

Unified equivalent frame method for flat plate slab structures under combined gravity and lateral loads - Part 2: verification

In the previous paper, authors proposed the unified equivalent frame method (UEFM) for the lateral behavior analysis of the flat plate structure subjected to the combined gravity and lateral loads, in which the rotations of torsional members were distributed to the equivalent column and the equivalent slab according to the relative ratio of gravity and lateral loads. In this paper, the lateral behavior of the multi-span flat plate structures under various levels of combined gravity and lateral loads were analyzed by the proposed UEFM, which were compared with test results as well as those estimated by existing models. In addition, to consider the stiffness degradation of the flat plate system after cracking, the stiffness reduction factors for torsional members were derived from the test results of the interior and exterior slab-column connection specimens, based on which the simplified nonlinear push-over analysis method for flat plate structures was proposed. The simplified nonlinear analysis method provided good agreements with test results and is considered to be very useful for the practical design of the flat plate structures under the combined gravity and lateral loads.

Unified equivalent frame method for flat plate slab structures under combined gravity and lateral loads - Part 1: derivation

The equivalent frame method (EFM) is widely used for the design of two-way reinforced concrete slab structures, and current design codes of practice permit the application of the EFM in analyzing the flat plate slab structures under gravity and lateral loads. The EFM was, however, originally developed for the flat plate structures subjected to gravity load, which is not suitable for lateral loading case. Therefore, this study, the first part of series research paper, proposed the structural analysis method for the flat plate slab structures under the combined gravity and lateral loads, which is named as the unified equivalent frame method (UEFM). In the proposed method, some portion of rotation induced in the torsional member is distributed to the flexibility of the equivalent columns, and the remaining portion is contributed to that of the equivalent slabs. In the consecutive companion paper, the proposed UEFM is verified by comparing with test results of multi-span flat plate structures. Also, a simplified nonlinear push-over analysis method is proposed, and verified by comparing to test results.

Finite Element Computational Modeling and Simulation Studies of Non-Penetrating Impact Using Fundamental Principles

A set of Mindlin plates bonded together is subjected to loading by impact, which is considered to represent a generic engineering structure and is analyzed through numerical simulation. The objective is to identify optimum configuration in terms of loading, structural dimensions, material properties and composite layup associated with micrometeorites impacts on spacecraft that will not penetrate into its structure. Following the algorithm developed for the problem, the work comprises an in-depth analysis of a generic flat plate structure subjected to impact and numerical simulation. The analyses are based on dynamic response with emphasis on the elastic region. The direct numerical simulation is carried out in parallel for the analysis, synthesis, parametric study and optimization. As simulation case study, the panel structure response to impact loading by a spherical rigid body at certain velocity perpendicular to the panel plate itself and numerical simulation is carried out as appropriate. Simulation results are validated through comparison with analytical work. The entire scheme carried out in this work is a novel comprehensive approach for the structural design of non-penetrated impact on metallic composites. The results show that the use of composites, in particular the bi-metallic composite, is instrumental in tailoring the plate materials to achieve non-penetrating impact.

Preliminary Collapse Simulation of a Reinforced Concrete Flat Plate Substructure Using Spring Connection Modelling

To investigate progressive collapse behavior of reinforced concrete (RC) flat plate structures, a reliable and efficient numerical approach is developed in this study using spring connection modelling. This connection unit aims to simulate complicate punching shear behavior at critical regions surrounding the columns. Five springs are used as the connection elements: two for flexural and integrity steel bars and three for concrete contributions. The flexural and integrity steel bars embedded in the columns are modeled explicitly, which enables the model to present the structural behavior post punching shear failure. Bending and shear actions are represented by two concrete springs. The third concrete spring is assigned axial action property to restrain two end nodes of the connection on the model. In particular, the punching shear spring controls the connection unit when punching shear failure occurs. To apply the connection unit, the regions of slab-column connections are partitioned from the slab regions according to the critical shear surfaces. Then the connection unit links two corresponding nodes on the two edges formed from the partition. A physical experiment of a RC flat plate substructure under progressive collapse is simulated. Result comparison demonstrates that the numerical model has the capability to capture the structural behavior in progressive collapse. However, further improvement of the modelling technique is necessary to enhance numerical accuracy.