Sandwich Deck Research Articles

A strain energy-based damage severity correction factor method for damage identification in plate-type structures

A strain energy-based damage identification method for plate-type structures is presented. The concepts of a damage location factor (DLF) matrix and a damage severity correction factor (DSCF) matrix, which can be derived from the elemental modal strain energy, are proposed. The damage identification method using the DLF and DSCF is developed for damage localization and quantification in plate-type structures. The method consists of three steps: sensitive mode selection, damage localization, and damage quantification. The proposed method is a response-based damage identification technique which requires the modal frequencies and curvature mode shapes before and after damage. Numerical study demonstrates its viability to correctly detect the damage, approximate the damage area, and estimate the damage severity under high measurement noise and low damage severity conditions. The possibility of damage identification using the partial modal strain energy from the modal strain/curvature mode shape in one direction of plate is also explored based on the numerically simulated data. The method is further implemented on the experimental modal testing data to identify damage at three stages of increasing damage severity on a fiber-reinforced plastic (FRP) sandwich deck panel using a surface-bonded PVDF sensor array. The present DSCF-based damage identification method, as demonstrated in this study, can be used as a viable and effective technique for damage localization and quantification of plate-type structures.

Interaction between web-core sandwich deck and hull girder of passenger ship

Structural response of modern large passenger vessels is fairly complicated due to discontinuities created by open spaces, but also due to balcony openings. These two facts result in non-linear strain distribution along the depth of the hull girder. During recent years steel sandwich panels have been developed to decrease the structural weight, centre of gravity of the ship and also to ease the production of the ships through modularity. In order to make decks, the sandwich panels need to be joined. In order to implement these panels to load carrying deck structures of the modern passenger ship their influence on the structural response of the hull girder needs to be investigated. Therefore, the present investigates the interaction between hull girder of passenger ship and steel sandwich decks. Sandwich decks with both symmetrical and production friendly non-symmetrical joints are considered and compared to the traditional decks made from stiffened plates. Both deflection and normal stresses are considered as the response.

Interaction between laser-welded web-core sandwich deck plate and girder under bending loads

Present paper investigates the interaction between laser-welded web-core sandwich deck plate and supporting girder under bending loads. The study is based on two linear-elastic Finite Element (FE) approaches, i.e. one using beam elements to model the girder and shell elements to model the homogenized web-core sandwich plate. With this approach the obtained FE model is considerably smaller than in the case of modeling the full, periodic, 3D geometry with shell elements. The FE solution results in stress resultants for beam and shell elements. These stress resultants do not describe accurately the periodic stress response of the sandwich plate or shear stress distribution at girder web. Therefore, the paper utilizes analytical methods to calculate these stress components from the obtained Finite Element solution. The second computational approach is based on modeling the actual 3D topology with shell elements. The two approaches are shown to be in very good agreement. The investigation shows that the effective flange width of the sandwich is different for the top and bottom face plates indicating that the interaction is different for these face plates. The present study also shows that this difference between the two faces depends strongly on the orientation of the web plates of the sandwich with respect to girder axis and the stiffness of the girder. The investigation also shows that the normal stress response in bending is dominated by the interaction between the sandwich plate and the girder, but also by the shear-induced normal stresses at the outer surface of the plate.

Evaluation of effective flange width by shear lag model for orthotropic FRP bridge decks

Abstract In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section with a reduced width of deck in relation to center-to-center spacing of stringers, over which the longitudinal normal stresses are assumed to be uniformly distributed, which is termed as effective flange width. It is defined in the AASHTO specifications primarily for concrete slabs and has inherent applicable limitations because of its empirical nature. This paper provides an analytical shear lag model for effective flange width for orthotropic bridge decks, applicable to various materials including Fiber-Reinforced Polymer (FRP) and concrete decks. To verify this solution, a Finite Element (FE) parametric study is conducted on 44 simply-supported FRP deck-on-steel girder bridges. The results from the shear lag model correlate well with the FE results. The accuracy of this model is further verified by close correlations with an existing empirical solution. It is also illustrated that the shear lag model, with the introduction of a reduction factor, can be applied to predict effective flange width for FRP deck-on-steel girder bridges with partial composite action, by favorable comparisons between the analytical and testing results for a T-beam section cut from a one-third scaled bridge model, which consists of an FRP sandwich deck attached to steel girders by mechanical connectors.

Structural performance of composite sandwich bridge decks with hybrid GFRP–steel core

Abstract This paper presents the static and fatigue performance of composite sandwich bridge decks with hybrid GFRP–steel core. The composite sandwich bridge deck system is comprised of wrapped hybrid core of GFRP grid and multiple steel box cells with upper and lower GFRP facings. Its structural performance under static loading and fatigue loading with a nominal frequency of 5 Hz was evaluated. The responses from laboratory testing were compared with the ANSYS finite element predictions. The failure mode of the proposed composite sandwich bridge deck was more favourable because of the yielding of the steel tube when compared with that of all-GFRP decks. The ultimate failure of the composite sandwich deck panels occurs by shear of the bonded joints between GFRP facings and steel box cells. Results from fatigue load test indicated no loss in stiffness, no signs of de-bonding and no visible signs of deterioration up to 2 million load cycles. The thickness of the composite sandwich deck retaining the similar stiffness may be decreased to some extent when compared with the all-GFRP deck. This paper also presents design of a connection between composite sandwich deck and steel girder.

Buffalo Creek Bridge: A case study of empirical versus traditional bridge deck design

This paper presents a case study of the Buffalo Creek bridge structure under two conditions, one with an empirical sandwich deck referred to as “old deck design” and the other with traditional deck referred to as “new deck design”. The focus of the study is to assess the performance of the empirically designed reinforced concrete bridge decks versus those designed using traditional analytical design methods and to check the adequacy of both design methods by correlating the theoretical results with field observations. For this purpose, two 3D finite element models of the old deck and new deck designs were developed together with the bridge superstructure. Both models were subjected to real life loading configurations of self weight and temperature variations. A comparison of the stresses induced in both models indicates that the stresses developed in the empirically designed concrete deck (old design) at the levels of the reinforcing mats are similar to those developed in the traditionally designed deck. The connections between the steel main girders and the concrete deck are the main constrains for deck expansion and contraction in the transverse direction, hence high tensile stresses were developed over the girders in the transverse direction. Additionally, the sharp edge of the clip angle protruding into the concrete deck as well as the top of the slope of the stay-in-place forms were identified as stress risers that contribute to the longitudinal cracking problem.

Strength evaluations of sinusoidal core for FRP sandwich bridge deck panels

Abstract Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal core geometry have shown to be successful both in new construction and the rehabilitation of existing bridge decks. This paper is focused on an experimental study of the strength evaluations of a honeycomb sandwich core under out-of-plane compression and transverse shear. The sinusoidal core is made of E-glass Chopped Strand Mat (ChSM) and Polyester resin. The compressive, tensile and shear strengths were first obtained from coupon tests. The out-of-plane compression tests were performed on representative single-cell volume elements of sandwich panels, and the tests included “stabilized” samples to induce compression failure, and “bare” samples to induce local buckling of the core. Finally, four-point bending tests were conducted to study the structural strength behavior under transverse shear. Two types of beam samples were manufactured by orienting the sinusoidal wave either along the length (longitudinal) or along the width (transverse). Both typical shear failure mode of the core material and delamination at the core–facesheet bonding interface were observed for longitudinal samples. The failure for transverse samples was caused by core panel separation. For both single-cell and beam-type specimen tests, the number of bonding layers, i.e., the amount of ChSM contact layer and resin used to embed the core into the facesheet, and the core thickness are varied to study their influence. The experimental results described herein can be subsequently used to develop design guidelines.

A study of the new construction method for transverse box culverts by using the steel‐concrete composite sandwich deck slab – cutting the cost of constructing expressways

AbstractExpressways are typically constructed on high embankments to accommodate transverse box culverts. If the embankment height could be reduced while still accommodating culverts, then the road construction costs could be lowered by reducing the required volume of embankment soil. The authors achieved this by devising a transverse box culvert whose steel‐concrete composite sandwich deck slab resembles the composite slabs used for road bridges.The slab was tested indoors for bending failure, punching shear failure and fatigue strength under cyclic wheel loading. It was tested in an expressway for loading by heavy vehicles. The experiments demonstrated the soundness of the design method.This paper describes the design and construction of this structure, and the results of the indoor and outdoor experiments.

Finite-Element Modeling and Development of Equivalent Properties for FRP Bridge Panels

Fiber-reinforced polymer FRP composite materials are increasingly making their way into civil engineering applications. To reduce the self-weight and also achieve the necessary stiffness, sandwich panels are commonly used for FRP bridge decks. However, due to the geometric complexity of the FRP sandwich deck, convenient analysis and design methods for FRP bridge deck have not been developed. The present study aims at developing equivalent properties for a complicated sandwich panel configuration using finite- element modeling techniques. With equivalent properties, the hollowed sandwich panel can be transformed into an equivalent solid orthotropic plate, based on which deflection limits can be evaluated and designed. A procedure for the in-plane axial properties of the sandwich core has first been developed, followed by developing the out-of-plane panel properties for bending behavior of the panel. An application is made in the investigation of the stiffness contribution of wearing surface to the total stiffness of bridges with FRP panels. The wearing surface contribution is not usually accounted for in a typical design of bridges with traditional deck systems.

Assembly and Stabilization of a Planar Tetracoordinated Carbon Radical CAl3Si: A Way To Design Spin-Based Molecular Materials

For traditional sandwichlike molecular materials, the spin properties are not governed by the closed-shell sandwich decks, but by the type of center atoms and by the interaction between the center atom and the deck. Here, on the basis of density functional theory calculations, we report a kind of 1D, 2D, and 3D cluster-assembled sandwichlike molecular materials [D(CAl3Si)M]q+, saturated compounds (Cl-)q[D(CAl3(Si)M]q+ (D = CAl3Si, Cp-(C5H5-); M = Li, Na, K, Be, Mg, Ca) as well as the extended frameworks, whose spins are purely determined by the planar tetracoordinated carbon (ptC) radical-deck (CAl3Si). To capture and stabilize the ptC radical, we proposed a scheme “heterodecked sandwich”, in which way CAl3Si can act as a spin-embedded “superatom” because of the well conservation of the radical's spin, structural and electronic integrity during the cluster assembly. This should represent the first attempt to assemble a spin-deck into the magnetic molecular materials, which provides a bridge between the planar carbon chemistry and the spintronics realm.

Cycling tests of a fibre-reinforced polymer honeycomb sandwich deck panel at very cold temperatures

The FRP deck panel with an overall geometry of 2.134×0.340×0.178 m was cyclically tested under a three-point loading setup in a cold room with the temperature as low as −55°C. The Classic Beam Theory (CBT) method and the Finite Element (FE) method were also used to predict the panel behaviour at room temperatures. Based on this research, the following conclusions were made: (1) The low-temperature stiffness was about 3.8% higher than at the high temperature as long as the low temperature was above a certain degree; (2) When the temperature was lowered from −20 to −55°C, the low-temperature stiffness decreased 11.5% comparing with the stiffness at room temperatures. This degradation in stiffness could not be recovered by raising the panel temperature; (3) During the ultimate load test at −55°C, the panel failed at 171.1 KN with a very loud noise. Visual inspections indicated the debonding of the face sheet finally led to the local buckling of the exterior plate on both sides of the panel; (4) Very cold temperature exposure resulted in matrix hardening, matrix micro-cracking and fibre-matrix debonding as demonstrated by the AE testing data at different temperatures; and (5) At the room temperatures, the FRP panel showed a little stiffer performance than both the CBT method and the FE method would predict.

FEA of Complex Bridge System with FRP Composite Deck

Innovative fiber-reinforced polymer (FRP) composite highway bridge deck systems are gradually gaining acceptance in replacing damaged/deteriorated concrete and timber decks. FRP bridge decks can be designed to meet the American Association of State Highway and Transportation Officials (AASHTO) HS-25 load requirements. Because a rather complex sub- and superstructure system is used to support the FRP deck, it is important to include the entire system in analyzing the deck behavior and performance. In this paper, we will present a finite-element analysis (FEA) that is able to consider the structural complexity of the entire bridge system and the material complexity of an FRP sandwich deck. The FEA is constructed using a two-step analysis approach. The first step is to analyze the global behavior of the entire bridge under the AASHTO HS-25 loading. The next step is to analyze the local behavior of the FRP deck with appropriate load and boundary conditions determined from the first step. For the latter, a layered FEA module is proposed to compute the internal stresses and deformations of the FRP sandwich deck. This approach produces predictions that are in good agreement with experimental measurements.

Buckling Behavior of Honeycomb FRP Core with Partially Restrained Loaded Edges under Out-of-plane Compression

Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal honeycomb core geometry have shown to be efficient in both new construction and rehabilitation of highway bridge decks. The sandwich panel consists of top and bottom laminated face sheets bonded to the honeycomb core, which extends vertically between face sheets. This paper is focused on the study of the buckling capacities of the core components under out-of-plane compression. The facesheet and core are attached by contact molding and are, therefore, not rigidly connected. Thus, this problem can be described as the instability of an FRP core panel with two rotationally restrained loaded edges. An elastic restraint coefficient is introduced to quantify the bonding layer effect between the facesheet and core, and a simple and relatively accurate test method is proposed to obtain the restraint coefficient experimentally. A combined analytical and experimental study of compression is presented. By solving a transcendental equation, the critical compression buckling stresses are obtained, and a simplified expression to predict buckling strength is formulated in terms of the elastic restraint coefficient. The analytical solution is verified by finite element (FE) analysis. Compression tests are carried out to evaluate the effect of the bonding layer thickness, and the experimental results correlate closely with analytical and FE predictions. A parametric study is conducted to study the core aspect ratio effect on the buckling load. The method described in this paper can be further extended to determine local buckling capacities of other structural shapes with elastic restraints along the loaded edges.

Experimental Validation of a Shear Stud Connection between Steel Girders and a Fiber-Reinforced Polymer Deck in the Transverse Direction

A fiber-reinforced polymer (FRP) deck-to-girder connection was evaluated for fatigue resistance and residual capacity in the transverse direction. The connection consisted of three shear studs cast into a trapezoidal cell of a FRP sandwich deck. Steel spirals were positioned around each shear stud to aid in grout confinement. Test fixturing consisted of multiple girders and tie downs to induce realistic loading of the connection due to wheel loads. The connection was fatigued according to AASHTO LRFD Specifications for 10.5 million cycles (75 year design life) and tested for residual capacity. The connection survived fatigue testing without failure. The haunch exhibited minimal debonding and cracking. Connection capacity after one lifetime of fatigue cycles exceeded strength limit state requirements.

Local effects in the vicinity of inserts in sandwich panels

The paper considers local bending effects induced in the vicinity of inserts in sandwich panels. Such local bending effects are associated with an increase of bending stresses in the sandwich faces and normal and shear stresses in the sandwich core. An earlier developed analytic model [Proceedings of the Sixth International Conference on Sandwich Structures (ICSS-6) (2002) 551] is adapted for the case of a sandwich panel with circular insert, with elastic properties differing from those of the core. The locally induced stresses in the faces and core due to presence of the insert are expressed via simple analytic relations (and charts) enabling an estimation of these local stresses. Finite element analysis is employed to demonstrate the applicability of the analytic model, and a good correspondence between the numerical and the analytical data is found. A study case related to marine applications, namely a circular insert in a sandwich deck panel used for mounting of a rigging fixture, is considered, and optimization of an existing design is carried out.

Use of modal energy distribution in the design of honeycomb sandwich decks

Through the example of a spacecraft equipment deck, which is generally made of honeycomb sandwich construction, it is shown that modal energy distribution can be used as an effective guideline in improving the deck's frequencies to meet the restrictions imposed upon it. The kinetic energy distribution is employed as a basis for redistributing various packages on the deck. Strain energy distribution is used to identify areas which can be stiffened by bonding ‘doublers’ on the face sheets and the doubler thickness is obtained from a sensitivity analysis.

The performance of model composite bridge decks constructed with open sandwich slabs

A new form of lightweight roadway deck for composite bridges utilising externally reinforced concrete is proposed. Tests to destruction on four quarter-scale model bridge decks incorporating both open sandwich and inverted catenary deck slabs are described. The choice of an appropriate adhesive to form the necessary shear connection between concrete and steel is vital. The three decks constructed with such and adhesive exhibited at collapse a factor of safety of three over design HB load. The fourth deck failed at twice the design load. With inverted catenary decks sufficient horizontal restraint is developed to reduce the crown bending moment to 30% of the expected in a simple beam, but the critical failure mechanism is punching shear. The open sandwich deck exhibited a ductile failure with extensive yielding of the soffit plate. Finite element calculations are shown to provide a reasonable prediction of behaviour within the elastic range.