Interior Support Research Articles

Shear behavior of externally prestressed precast concrete segmental beams with both positive and negative moment regions

To investigate the shear behavior of externally prestressed precast concrete segmental beams with both positive and negative moment regions (EPCS P&N beams), eight specimens were subjected to failure under various shear span to depth ratios, moment ratios, and joint types. Throughout the testing process, critical crack initiation and development, joint slippage and opening, failure processes and modes, as well as strains in concrete, stirrups, and external prestressing tendons were meticulously recorded. At the point of failure, the concrete in the shear-compression zone near the top surface of the joint section (closest to the loading point in the positive moment region) or near the bottom surface of the joint section (closest to the interior support in the negative moment region) experienced crushing. Subsequently, the external tendons lost support and underwent elastic retraction, causing the two segments on either side of the critical web-shear crack to slide against each other. The elastic strain energy was released significantly as a consequence of the external tendons retracting, leading to the rupture of stirrups intersecting the failure cracks, followed by flange buckling. Based on the test results, a strut-and-tie model was developed to analyze the shear resistance mechanism, and a detailed flowchart for computing the shear resistance of EPCS P&N beams was established. The predictions from the proposed analytical method were compared with the test results, showing good agreement and confirming the rationality of the proposed shear resistance mechanism.

GFRP continuous RC beams having web openings and externally strengthened with CFRP composites

With the enormous development of modern buildings, it is highly required to accommodate web openings in continuous reinforced concrete (RC) beams for passing utility service equipment. A wide range of studies had been conducted with regard to this subject. wtCurrent study examined numerically the major effect of the large rectangular web openings in (GFRP) reinforced concrete continuous beams under concentrated loads. Moreover, it investigated the effects of different CFRP strengthening schemes that would retrieve the ultimate capacity of the solid beam. Based on that, the main parameters that had been utilized here are the opening size, opening location and the strengthening scheme. Results showed that openings reduced the ultimate load capacity of the beams and increased the overall deflections. Furthermore, using CFRP sheets to strengthen continuous RC beams including opening retrieved (70%) of the ultimate capacity of continuous RC solid beams especially beams with openings near the external support or midspan. Likewise, using CFRP composites retrieved (48%) of the ultimate capacity of continuous RC solid beams with openings near the interior support. Furthermore, the optimum location for constructing web openings was near the external supports, which was subjected to the lowest values of shear forces and sagging moments and leaded to accommodate greater ultimate loads (85.18 kN) than other beams of other openings location.

ARCHITECTURAL, INTERIOR DESIGN, AND TECHNOLOGICAL INTERVENTIONS TO FACILITATE REHABILITATION AND AGING IN PLACE

Abstract Most older adults 60 years and above live in the community with either support from their caregivers or independently. Aging in place successfully involves safely carrying out activities of daily living at home without accidents and injuries. However, most traditional homes are not equipped with safe interior designs or support technological interventions, which could be a barrier to aging in place. We performed a narrative review to understand the importance of incorporating architectural, interior design, and technological interventions to support the rehabilitation of older adults with disabilities to successfully age in place. We reviewed 28 research papers from several research databases matching the inclusion criteria on interventions targeting older adults’ rehabilitation outcomes. We included studies that focused on various health conditions (e.g., spinal cord injury, stroke) and supporting home modification along with technological interventions. The review shows that the home environment has a significant impact on older adults’ overall health, and recovery, including functional capacities, cognitive processes, and emotional states providing autonomy, safety, and accessibility. Several safe design features were found, including barrier-free entrance, mobile stair climber, handrails and grab bars, anti-skid flooring, open layout, and shower seat. The integration of technologies (e.g., sensor lights, voice-activated devices) was identified as a promising avenue for enhancing the quality of life. Co-designing the built space with older adults was found to be effective. Our review highlights the need for collaboration between healthcare professionals, engineers, architects, and policymakers to design existing or new homes that support safe aging in place of older adults.

Flexural behavior of externally prestressed continuous steel-concrete composite beams

To investigate the flexural behavior of continuous externally prestressed steel–concrete composite (EPSCC) beams, flexural tests were conducted on two two-span continuous beams with a total length of 9.8 m. The test parameter focused on the number of deviators in each span. With the aid of detailed measurement of deviator displacement, slip distribution on the steel-slab interface and strain along shear connectors, the shear mechanism of headed studs and the second-order effect in continuous EPSCC beams were evaluated. The test results indicated that both beams underwent concrete cracking over their interior supports, followed by the formation of a plastic hinge in the hogging moment zone, the subsequent formation of a plastic hinge in the sagging moment zone, and ultimately the crushing of concrete slabs in the sagging moment zone. Prior to failure, full plasticity was developed at both the mid-span section and interior support section of each beam. The local moment acting on the shear studs reached its maximum hogging values at the shank root, while its maximum sagging value was attained at approximately the mid-height of the shank. Due to the second-order effect, the removal of deviators at midspans resulted in a 7.1% decrease in the sagging moment of the beam. At the ultimate limit state, the measured degree of moment redistribution values for hogging moment ranged between 52% and 58%, which were higher than the specified limits in current design guidelines. The predictions of the ultimate hogging and sagging moment calculated from plastic theory were consistent with experimental results.

Design Procedures for Predicting Long-Term Responses of Continuous Steel–Concrete Composite Slabs

Although the effect of nonuniform shrinkage on the time-dependent behavior of simply supported composite slabs has been extensively investigated, continuous composite slabs have not garnered enough attention. This paper aims to propose the routine design procedures for continuous composite slabs, including the hogging moment over the interior support and the mid-span deflection. Thus, the long-term test data on two-span continuous composite slabs provided by the authors and the related literature were collected to benchmark the current design methods in international specifications. The routine design procedures for calculating the long-term moment distribution and the mid-span deflection of two-span composite slabs were proposed considering the time-dependent range of hogging moment zones. Moreover, the effects of different shrinkage distributions and hogging moment ranges on the long-term performance of these slabs were further quantified. The results showed that the mid-span deflection and the hogging moment over the interior support increased significantly over time; both could not be accurately predicted using the typical design methods described in international specifications. The hogging moment declined by 28.0% when a uniform shrinkage profile was adopted for the design of composite slabs, and the mid-span deflection decreased by 15.0% when a constant range of the hogging moment zones was used. The design procedures proposed herein well described the long-term behavior of continuous composite slabs by accounting for the combined effects of the nonuniform shrinkage and time-dependent hogging moment range. The calculated hogging moment and mid-span deflection differed from the measured ones on average by 2.0% and 9.0%.

Modal analysis of power law functionally graded material plates with rectangular cutouts

This article aims to analyze rectangular functionally graded material plates with rectangular cutouts of diverse sizes, numbers, and positions for free vibration using Mindlin’s first-order shear deformation theory (FSDT). Isoparametric plate elements of nine nodes and five degrees of freedom at each node were used for the present finite element formulation. The Poisson ratio is assumed to be constant throughout the plate. At first, results piled up from the present finite element formulation were compared with existing results collected from various previous journals for different isotropic plates and functionally graded material plates. After verification of finite element formulation, some new results (nondimensional fundamental frequency) were obtained considering various shapes, sizes, numbers, positions of cutouts, thickness ratio, aspect ratio, FGM power law index, and different edge conditions. Dynamic analysis of FGM plate with interior support along rectangular cutout edges is an integral part of this study.

Experimental Investigation on The Transform The Simply Supported Girders to Continuous Girder by Using The UHPC Cast in Place Joint

Many bridges are made from multi-simple spans and can be enhanced by transforming into a continuous girder. An experimental program investigated the transformation of the simply supported girder to a continuous girder using the ultra-high performance concrete (UHPC) joint. The transformation process was presented by arranging a negative reinforcement and cast in place the deck with joints to ensure the continuity of the segment through the interior support. This study presents the material properties, preparation of specimens, the cast of normal strength concrete (NSC) and UHPC, and tested the girder with a point load. The parameters of this study included the support condition, type of joint, hybridization of top reinforcement, and type of load (monotonic and cyclic load). The results showed that the continuous support increased the load-carrying capacity by about 21.4% and reduced the service mid-span deflection by about 24.3% concerning simply supported having the same clear span and section geometry. The effect of using the shear key and carbon fiber reinforced polymer CFRP rebar was presented. This study discussed failure mode, cracking propagation, initial stiffness, and flexural ductility to understand the structural behavior of continuous splice girder. As a result of these investigations, suggestions were identified for future research.

Creating interior support structures with Lightweight Voronoi Scaffold

Nowadays product designers have possibilities to design complex geometries, since for instance with additive manufacturing, there is less technological limits then before. However, besides that they have geometric freedom, it is essential to pay attention to engineering aspects, such as efficient material usage, stiffness and so on. This article is dealing with internal support structures and introduces a new lattice, called Lightweight Voronoi Scaffold. The scaffolds as 3-dimensional structures are well known in numerous fields of science. These structures provide mechanical stiffness for bones and place for biomolecules as well. The aim of this research was testing this new structure in case of complex geometry with multiaxial load case. Therefore, the arrangement of Voronoi scaffold is not regular, random sampling-based Monte Carlo method was applied in order to provide proper distribution of generation of geometric instances. Although the random point seed generates a high number of improper geometries, the remaining ones always include notable solutions. Lightweight Voronoi Scaffold was compared to some common regular beam lattices, and results shown that Lightweight Voronoi Scaffold was lighter in each case, that may open new opportunities in the field of additive manufacturing.

Structural behavior of continuous two-span prestressed concrete T beams with different tendon profiles

Approximately half-scale tests were conducted to inves­tigate the behavior of indeterminate prestressed concrete T beams with two different unbonded tendon profiles. Three T beams were employed for the tests: T beam specimen 1 (TB1) was the control specimen and had no eccentricity at the interior support and T beam speci­mens 2a and 2b (TB2a and TB2b) had eccentricity at the interior support. The results indicate that the specimens with eccentricity at the interior support had a greater number of cracks than the control specimen at the ten­sion zone of the support. This finding was explained by hyperstatic moment reducing the negative moment in the control. The trend in the slope of the strain-applied load tension relationship was different in TB1 than in TB2a due to a difference between the specimens in terms of the distance from the extreme compression fiber to the centroid of reinforcement at the support. Although the interior support was a roller with no vertical restraint, hyperstatic moment at the support occurred due to a cold welding effect, creating a partial roller condition. The hyperstatic action then decreased as the loading was increased. The authors conclude that the effect of hyperstatic moment should be accounted for in the calculation of concrete stress at the service level for continuous prestressed concrete beams with unbonded tendons and a vertically unconfined support condition.

Localization of travelling and standing waves in a circular membrane coupled to a continuous viscoelastic support

We present an analytical approach for realizing the localization of travelling and standing waves in a circular membrane by means of an interior, continuous, ring-type viscoelastic support when the membrane is subjected to harmonic boundary excitation. This work is a continuation of the wave separation dynamics induced by nonclassical damping in one-dimensional elastic continua. For a two-dimensional azimuthally symmetric configuration, a necessary and sufficient condition is established to realize wave localization, leading to uniformly distributed spring stiffness and damping coefficients for the interior support. A rotating wave localization pattern can also be realized by applying a circumferentially moving boundary excitation. The desired results are shown to depend strongly on the excitation frequency, the circumferential wavenumber, and the radius of the continuous support. For a weakly eccentric configuration with uniformly distributed boundary excitation, non-uniform required distributions of the support properties can be obtained analytically. However, waveform distortion will occur for either non-uniformly distributed boundary excitation with weak support eccentricity or highly eccentric coupling, such that the parameter values of the support have zero crossings on the nodal diameters of the membrane and thus lose physical meaning. The results presented in this work are expected to be useful in the design of mechanical and acoustic systems to localize energy to a sonic bullet by means of the continuous distribution of damping.

Probabilistic Assessment of Bending Strength of Statically Indeterminate Reinforced Concrete Beams

This paper presents a reliability analysis of a two-span reinforced concrete beam, taking into account of random variations in cross-sectional dimensions, area and position of reinforcement for sagging and hogging bending moments, material strengths, loads and model uncertainties. In addition, the limit state functions for the statically indeterminate beam were derived; considering the static equilibrium requirement after the moments were redistributed as well as the codified allowable limit for the adjusted moment at each beam section. A large number of Monte Carlo simulations were performed in which the basic variables were modeled with normal, lognormal and Gumbel distributions. When the elastic moment distribution was used in evaluating the beam reliability, the two-span beam behaved as a series system with three critical nodes located at the interior support and midspan sections. The probability that the system had at least one overloaded node was greater than the failure probability of an individual node. However, considering moment redistribution made it possible to reduce the amount of reinforcement whilst maintaining the reliability of the beam. When the reinforcement area was reduced by 26% at the support section or 14% at the midspan sections, the failure probability was predicted to be 6.90´10-5, which is deemed acceptable for a 50 year reference period.

The Construction of Conforming-to-shape Truss Lattice Structures via 3D Sphere Packing

Truss lattices are common in a wide variety of engineering applications, due to their high ratio of strength versus relative density. They are used both as the interior support for other structures, and as structures on their own. Using 3D sphere packing, we propose a set of methods for generating truss lattices that fill the interior of B-rep models, polygonal or (trimmed) NURBS based, of arbitrary shape. Once the packing of the spheres has been established, beams between the centers of adjacent spheres are constructed, as spline based B-rep geometry. We also demonstrate additional capabilities of our methods, including connecting the truss lattice to (a shell of) the B-rep model, as well as constructing a tensor-product trivariate volumetric representation of the truss lattice — an important step towards direct compatibility for analysis.

Improved method for shear lag analysis of thin-walled box girders considering axial equilibrium and shear deformation

Abstract The conventional method (CM) for shear lag analysis of thin-walled box girders supposes that the neutral axis coincides with the centroidal axis of the whole cross section, and thus neglects the axial equilibrium condition. An analytical method considering axial equilibrium and shear deformation, which is referred to as PM, is proposed for overcoming the defect of the conventional method. The longitudinal displacement of the web is introduced to satisfy the axial equilibrium condition and locate the neutral axis automatically. The shear deformation is considered according to the Timoshenko beam theory. Three independent shear lag functions are adopted for describing different shear lag intensities of the top, bottom and cantilever slabs. The governing differential equations for the displacement variables are deduced by means of the virtual work theorem and solved with the relevant boundary conditions. The analytical solution is then derived for the distance from the neutral axis to the top fiber of the cross section. The accuracy of the proposed method is validated by comparisons with the available experimental data as well as the finite element analysis results. Moreover, the distances from the neutral axis to the top fiber, axial forces, and stress difference ratios are analyzed for typical thin-walled box girders to quantify the influence of the axial equilibrium condition. Finally, an extensive parametric study is conducted to examine the effects of various geometric parameters on the stress difference ratio under different load types. The results show that the proposed method can provide good predictions for both deflections and axial stresses, and neglecting axial equilibrium leads to considerable underestimations of axial stresses especially at the top flange-web junctions over the interior support of the continuous box girder.

Long-term behavior of continuous composite slabs made with 100% fine and coarse recycled aggregate

A composite slab is an efficient modern structural member. Recycled fine and coarse aggregates are alternative green materials for the depleting natural sand and natural gravels in the composite slabs. In recent years, the nonuniform shrinkage occurring in single-side-exposed concrete has been discovered to significantly affect the long-term behaviors of composite slabs, which have been included in newly published codes. Applying recycled aggregate concrete (RAC) would further increase the effect of nonuniform shrinkage on the long-term behaviors of composite slabs. However, most studies, with RAC or not, have only focused on simply- supported composite slabs. For continuous composite slabs (CCSs), in addition to increasing deflections, a nonuniform shrinkage would induce a larger negative bending moment, which would further increase the crack width at the interior support region. Hitherto, no experiment has been conducted regarding the time-dependent crack width of CCSs and CCSs with RAC. Therefore, the aim of this study is to investigate the effects of nonuniform shrinkage and RAC on the deflections, strains, and cracks of CCSs. Hence, a 500-d experiment was conducted on three full-scale specimens. Finally, a finite element (FE) model was established and benchmarked against the test results of this study and those reported in the literature. The results indicated that (1) nonuniform shrinkage significantly increased the crack width at the negative bending moment region; (2) the use of RAC resulted in a more significant effect of the nonuniform, e.g. mid-span deflections, soffit strains, and crack widths increased by 40%, 64%, and 38%, respectively; and (3) the FE model can predict the long-term behaviors of CCSs well.

Moment redistribution in continuous steel-fibre-reinforced concrete slabs

The phenomenon of moment redistribution in steel-fibre-reinforced concrete (SFRC) members has not been adequately studied. In this study, the phenomenon was investigated by conducting point-load tests on seven two-span, one-way continuous slabs without traditional reinforcement. Significant redistribution of moments from the elastic values was observed at the critical mid-span and interior support sections. An analytical approach to predict the moment–curvature response of SFRC is presented, with which the predicted variation of moments with increasing load compared to the observed trends with reasonable accuracy. Also, the analytical approach predicts the load-carrying capacity of the slabs within 8% of the average observed values, with a standard deviation of 8%. In addition, the load–deflection curves of the slabs were well predicted. The results are beneficial for the analysis and design of a SFRC slabs-on-pile system by considering moment redistribution due to slab continuity.

Co-existing complexity-induced traveling wave transmission and vibration localization in Euler-Bernoulli beams

We analytically and numerically examine the dynamic behavior of an undamped, linear, uniform and homogeneous Euler-Bernoulli beam of finite length, partially supported in its interior by local, grounded, linear spring-dashpot pairs and subjected to a harmonic displacement at its pinned left boundary or at both its ends. The Euler-Bernoulli beam is known to be dispersive and, thus, to exhibit a non-constant relationship between frequency and wave number. Local dissipation due to the interior support results in a non-classically damped system and, consequently, mode complexity. An analytical framework is developed to examine the coexistence of propagating and standing harmonic waves in complementary regions of the beam for four distinct boundary conditions at the right end: pinned, fixed, free and linear elastic. We show that the system can be designed so that, for a particular input frequency and interior support location, nearly perfect spatial separation of traveling and standing waves can be achieved; the imperfection is shown to be caused by the non-oscillatory evanescent components in the solution. We further demonstrate that vibration localization is achieved by satisfying necessary and sufficient wave separation conditions, which correspond to frequency- and position-dependent support stiffness and damping values, and that linear viscous damping in the interior support, but not necessarily linear stiffness, is required to achieve the separation phenomenon and vibration localization.

Optimization of process planning for reducing material waste in extrusion based additive manufacturing

• The influences of printable threshold overhang angle (PTOA) and longest printable bridge length (LPBL) on support consumption are discussed. • A new support generation method is proposed based on the features of printable threshold overhang angle and longest printable bridge length. • Three parts were printed for verifying that the proposed support method can save more material, print time and energy consumption. Among the available additive manufacturing technologies , extrusion based 3D printing (otherwise known as fused deposition modelling or fused filament fabrication) is among the most commonly used due to low cost and relative simplicity. However, such printers still suffer from redundant support material waste (both interior and exterior) when printing large-volume solid objects or objects with overhangs. The support material can also be a significant cause of long part production time and higher energy consumption during manufacture. Hence, we propose a new support generation strategy considering both interior and exterior support via AM process planning to reduce the total amount of material consumption, production time and energy consumed for manufacturing an object. Print path and print orientation are both considered as significant factors and are both optimized for achieving the lowest consumption of material. The areas to be filled on each layer are determined according to the printable threshold overhang angle (PTOA) and the longest printable bridge length (LPBL). The characteristics of LPBL and PTOA are fully considered for saving more material. Several tests are used to verify the proposed strategy and the results show that this strategy can considerably reduce material waste, production time and energy consumed compared with conventional strategies, enabling AM to be a more environmentally friendly and sustainable manufacturing technique.

Strong 3D Printing by TPMS Injection.

3D printed objects are rapidly becoming prevalent in science, technology and daily life. An important question is how to obtain strong and durable 3D models using standard printing techniques. This question is often translated to computing smartly designed interior structures that provide strong support and yield resistant 3D models. In this paper we suggest a combination between 3D printing and material injection to achieve strong 3D printed objects. We utilize triply periodic minimal surfaces (TPMS) to define novel interior support structures. TPMS are closed form and can be computed in a simple and straightforward manner. Since TPMS are smooth and connected, we utilize them to define channels that adequately distribute injected materials in the shape interior. To account for weak regions, TPMS channels are locally optimized according to the shape stress field. After the object is printed, we simply inject the TPMS channels with materials that solidify and yield a strong inner structure that supports the shape. Our method allows injecting a wide range of materials in an object interior in a fast and easy manner. Results demonstrate the efficiency of strong printing by combining 3D printing and injection together.

Epidemiology of injury patterns for 4- to 10-year-olds in side and oblique impacts

Objectives: With regard to the pediatric population involved in vehicle side impact collisions, epidemiologic data can be used to identify specific injury-producing conditions and offer possible safety technology effectiveness through population-based estimates. The objective of the current study was to perform a field data analysis to investigate injury patterns and sources of injury to 4- to 10-year-olds in side and oblique impacts to determine the potential effect of updated side impact regulations and airbag safety countermeasures.Methods: The NASS-CDS, years 1991 to 2014, was analyzed in the current study. The Abbreviated Injury Scale (AIS) 2005–Update 2008 was used to determine specific injuries and injury severities. Injury distributions were examined by body region as specified in the AIS dictionary and the Maximum AIS (MAIS). Children ages 4 to 10 were examined in this study. All occupant seating locations were investigated. Seating positions were designated by row and as either near side, middle, or far side. Side impacts with a principal direction of force (PDOF) between 2:00 and 4:00 as well as between 8:00 and 10:00 were included. Restraint use was documented only as restrained or unrestrained and not whether the restraint was being used properly. Injury distribution by MAIS, body region, and source of injury were documented. Analysis regarding occupant injury severity, body region injured, and injury source was performed by vehicle model year to determine the effect of updated side impact testing regulation and safety countermeasures. Because the aim of the study was to identify the most common injury patterns and sources, only unweighted data were analyzed.Results: Main results obtained from the current study with respect to 4- to 10-year-old child occupants in side impact were that a decrease was observed in frequency of MAIS 1–3 injuries; injuries to the head, face, and extremities; as well as injuries caused by child occupant interaction with the vehicle interior and seatback support structures in 1998 model year passenger cars and newer.Conclusions: Results from this study could be useful in design advances of pediatric anthropomorphic test devices, child restraints, as well as vehicles and their safety countermeasure systems.

Long-Term Behaviour of Precast Concrete Deck Using Longitudinal Prestressed Tendons in Composite I-Girder Bridges

Twin-I girder bridge systems composite with precast concrete deck have advantages including construction simplification and improved concrete strength compared with traditional multi-I girder bridge systems with cast-in-place concrete deck. But the cracking is still a big issue at interior support for continuous span bridges using twin-I girders. To reduce cracks occurrence in the hogging regions subject to negative moments and to guarantee the durability of bridges, the most essential way is to reduce the tensile stress of concrete deck within the hogging regions. In this paper, the prestressed tendons are arranged to prestress the precast concrete deck before it is connected with the steel girders. In this way, the initial compressive stress induced by the prestressed tendons in the concrete deck within the hogging region is much higher than that in regular concrete deck without prestressed tendons. A finite element analysis is developed to study the long-term behaviour of prestressed concrete deck for a twin-I girder bridge. The results show that the prestressed tendons induce large compressive stresses in the concrete deck but the compressive stresses are reduced due to concrete creep. The final compressive stresses in the concrete deck are about half of the initial compressive stresses. Additionally, parametric study is conducted to find the effect to the long-term behaviour of concrete deck including girder depth, deck size, prestressing stress and additional imposed load. The results show that the prestressing compressive stress in precast concrete deck is transferred to steel girders due to concrete creep. The prestressed forces transfer between the concrete deck and steel girder cause the loss of compressive stresses in precast concrete deck. The prestressed tendons can introduce some compressive stress in the concrete deck to overcome the tensile stress induced by the live load but the force transfer due to concrete creep needs be considered. The concrete creep makes the compressive stress loss and the force redistribution in the hogging regions, which should be considered in the design the twin-I girder bridge composite with prestressed precast concrete deck.