Addition Of Stiffeners Research Articles

Residual stresses in steel I-sections strengthened by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is a method of metal 3D printing that can be used to complement traditional steel manufacturing techniques (e.g. hot-rolling and cold-forming), to produce hybrid structural elements of enhanced efficiency. The case of hot-rolled steel I-sections strengthened by the addition of WAAM stiffeners at the flange tips is the focus of the present study. In addition to the improved local buckling resistance and increased flexural rigidity achieved by the addition of the stiffeners, a further source of enhanced load-bearing capacity arises from the inversion, through thermal action, of the adverse residual stress pattern typically associated with hot-rolled I-sections. Thus, in contrast to previous studies, the aim of the present investigation is not to eliminate but to take benefit from residual stresses, by prestressing (pretensioning) specific parts (i.e. the flange tips) of steel sections against subsequent applied compressive loading, thereby delaying yielding and enhancing the load-bearing capacity. The described hypothesis is demonstrated in the present study through the manufacture of a series of hybrid WAAM-strengthened hot-rolled I-sections and the subsequent performance of residual stress measurements. Stiffeners of different dimensions were printed using ER70S-6 welding wire. A detailed description of the adopted experimental technique, which utilised the sectioning method, is provided, while the magnitude and distribution of the measured residual stresses are reported. The addition of WAAM stiffeners at the flange tips of hot-rolled I-sections is shown to lead to the generation of desirable (for structural stability) tensile residual stresses in their vicinity, with peak values reaching the yield strength of the material; self-equilibrating compressive residual stresses are induced in the web and around the web-to-flange junction.

Numerical Study of Castellated Beam with Stiffener – Case on Cantilever Structure

A castellated beam is designed to increase the depth of the beam by slicing the beam web longitudinally in a specified form and re-unite both pieces using welding to obtain a higher flexural capacity of the beam. Due to the increase in cross-sectional height and the presence of openings in the web plate, some potential failures may occur, for example buckling of the web and stress concentration on the opening. Addition of stiffener on the web is useful to prevent those potential failures. This paper presented a numerical study of castellated beam with additional stiffeners which is applied on a cantilever structure using MSC Nastran software. The castellated beam was added by stiffeners placed on three different zones. There were stiffeners on the perimeter of opening, on the web between openings, and on the web of opening. The cantilever beam was subjected by a point load increased monotonically until ultimate condition reached. It was found that applying of the stiffeners on perimeter of opening will increase ultimate load up to 7.48 % comparing to the original castellated beam. On contrary, stiffeners on the web between openings and the web of opening will decrease the ultimate load within the range of 0.40% - 4.86 %. The beam stiffness will slightly increase because of these three types of additional stiffeners. Regarding ductility of the beams, adding of stiffeners on the castellated beam showed vary numbers. Overall, the stiffeners on perimeter of opening become an alternative to increase the performance of the castellated beam in term of the ultimate load, beam stiffness and ductility.

Buckling analysis of stiffened FGM plates

The addition of stiffeners is a common way to achieve higher strength for plates. The linear buckling response of stiffened Functionally Graded Material (FGM) plates is investigated in this work. FGM plates having a centrally attached stiffener plate are subjected to in-plane uniform uniaxial loads. The gradation of material properties in FGM plates along the plate thickness is based on power-law, sigmoid and exponential functions. The critical buckling loads are obtained using finite element method based on Classical Plate Theory in ABAQUS software. The influence of material, plate aspect ratio, stiffener depth and width is studied in detail.

On the analysis of coupling strength of a stiffened plate-cavity coupling system using a deterministic-statistical energy analysis method

This paper combines the Impedance Mobility Compact Mothed (IMCM) with Statistical Energy Analysis (SEA) method to develop analytical structural-acoustic approach for analysis of a plate-cavity coupling system. The coupled system is composed of an acoustic cavity covered with a rectangular flexible plate that is stiffened by a beam integrated to the inner surface of the plate to modify the coupling strength between the plate and the air inside the cavity. This paper discloses the relationship between the coupling strength and coupling quotient. The results of the study indicate that the coupling strength between the plate and acoustic cavity can be determined by the natural frequency proximity and the matching degree of the mode shapes of the plate and acoustic cavity. Addition of stiffener onto the plate, increase of the plate thickness or decrease of the cavity volume will reduce the coupling strength. The newly proposed coupling coefficient can better quantify the coupling characteristics of the plate and cavity system in the low-middle frequency ranges. The results assessed by the proposed coupling coefficient have been verified by those assessed by the previously defined coupling coefficient and the coupling quotient in the SEA model in the high frequency range.

Anti-collapse performance analysis of unequal span steel–concrete composite substructures

In the study, three 1:3-scale unequal span steel–concrete composite substructures with top-seat angle and double web angle connection were designed and identified as specimens GTSDWA-0.6, GTSDWA-1.0, and GTSDWA-1.4. Pseudo-static tests and refined numerical model analysis were conducted to examine the anti-progressive collapse performance of a semi-rigid steel–concrete composite substructure. The results indicated that the failure modes of the three specimens revealed that the fracture occurred in the root of the long leg of the top/seat angle in tension at the connection. With increases in the span ratio of the left and right composite beams, the bearing capacities of the composite substructures decreased, and the corresponding displacement increased. With respect to GTSDWA-0.6 and GTSDWA-1.4, the resistance due to the short composite beam corresponded to 62% and 60%, respectively, and the total resistance provided by the short composite beam exceeded that of the long composite beam. With respect to GTSDWA-1.0, the resistance due to the left and right composite beams was similar. All three specimens underwent the flexure mechanism and flexure–axial mixed mechanism stages. They resisted the external load mainly via the flexure mechanism. Moreover, the addition of stiffeners on both sides of the top and seat angles is advantageous in terms of improving the collapse resistance and ductility of unequal span composite substructures.

Enhancing Structural Stability of Submerged Cylindrical Shell with Stiffeners

An extensive study is made on the buckling types and conditions of various types cylindrical shells based on their design and material properties. Based on those, numerical analysis is done on a submerged type of cylindrical shell. This analysis is done based on two different conditions. The first one includes design with the addition of stiffeners and the other is based on the design which has no stiffeners. A comparative study is performed between these two and the results are analyzed. Two cylindrical shells, one including stringer and the other without a stringer are modeled using CATIA with specific dimensions. These models are imported into ANSYS to perform an explicit dynamic analysis. Parameters such as equivalent stress, equivalent elastic strain, shear stress, shear elastic strain and total deformation are calculated. The end results are obtained using ANSYS and the graphs are plotted using the values obtained. Based on the results obtained, it is concluded that the use of stiffeners makes the structure widely enviable to bear compressive types of loads. Also, it gives additional strength to the structure with sturdiness at the top and bottom layers. Based on the study, it can be concluded that the use of rectangular type stringer is preferred much more than the other types.

Weak axis response of steel I-sections subjected to close-in detonations

The response of I-shaped, or wide-flange, sections subjected to close-in detonations has been evaluated through numerical simulations. A simulation approach for close-in detonation, which includes two stages, is suggested. The first stage includes the modelling of the detonation process through computational fluid dynamics (CFD) and the second stage includes only the free vibrations of the structural member. The suggested approach is validated by a comparison with two experimental results for close-in detonations. Then, a parametric study for I-sections with their weak axis subjected to close-in detonations has been performed. Various spherical charges and standoff distances have been studied, with scaled distances in the range of 0.15–0.29 m/kg1/3. Bare members and members strengthened with stiffeners have been simulated. The influence of charge and standoff distance, and the addition of stiffeners on several parameters affecting deformation and folding angles, has been studied. The effect of localized pressure confined between the flanges and the stiffeners at the midspan, which can lead to increased total and local deformations, is illustrated. Finally, an alternative strengthening method, in which the flanges are connected with bars, is presented as an optional stiffening technique.

Numerical Investigation of Bolted Hybrid Steel-Timber Connections

Hybrid steel to timber connections are found in many buildings and bridges. These connections offer several advantages such as ease of construction and energy dissipation. This research paper aims to study the mechanical behaviour of bolted hybrid connections that consists of a square hollow steel column (SHS) and a glulam timber beam. The connection between the two structural members is achieved by means of angles and preloaded bolts. A reference model is constructed and verified by comparison to experimental and numerical data from the international literature. Additionally, several parameters that affect the response of the connection are modified in order to investigate and quantify their effect, resulting in seven different case studies. These parameters are the size of the bolts, the thickness of the angles and the addition of stiffener. The moment- rotation curve of each case study is constructed and the results are commented. Finally, a proposed optimal configuration of the hybrid connection is presented.

Seismic Requirements for the Welding and Inspection of the K-Area in Hot Rolled Products to AS/NZS 3679.1

Hot-rolled products such as beams are usually subject to rotary straightening as a last step in the manufacturing process. This operation may change the properties of the plastically deformed area by strain hardening. The affected regions of the beam are referred to as the “k-area”, as shown in Figure 1. Strain hardening reduces the ductility and notch toughness of the steel and can potentially lead to cracking in the k-area when welding is carried out in restrained conditions e.g. addition of stiffeners by welding. The phenomenon was reported for wide flange beams in the US literature in the 1990s. Welding limitations and increased inspection requirements in these areas were introduced to AISC and AWS D1.8 codes [1]. Similar requirements can be found in New Zealand Standard NZS 3404.1 [2]. However, it is unclear if steel products used in New Zealand are affected by this phenomenon. A series of welding and performance tests were carried out at HERA using hot rolled products UB610, UC310, UB310 and UC200 of material grade 300S0 to AS/NZS 3679.1 [3]. The material is commonly used in New Zealand for seismic construction. Welded test specimens were subject to a range of testing, including mechanical and cold cracking susceptibility tests. Test setup and results are reported in the paper. The authors present recommendations for future standard developments.

Development of a building integrated solar photovoltaic/thermal hybrid drying system

This work presents a feedback of the main experimental studies performed on a solar PV/T hybrid air collector, from optimization to demonstration. Indoor experimental parametric studies permitted to optimize the system basic configuration consisting in a PV laminate inserted into a metal absorber and comprising an insulated air gap at the underside. The main results showed that the modification of the system configuration leads heat rise in PV laminate and thus to the decrease of its electrical performance. The main solution proposed was the addition of stiffeners at the absorber backside in order to optimize its heat transfer surface with the PV laminate. The optimized prototype was, then, integrated into a roof fodder drying installation in Savoy. First thermal, electrical and aeraulic measurements showed that wind velocity has an important effect on air velocities in the air gap, even in drying periods. Considering the existing air gap and indoor tests results, the system daily thermal efficiency up to 27.7%, the PV field electrical efficiency up to 13% and the maximum air preheating of 7.8 °C indicated that the PV/T system is suitable for fodder drying application. As further studies, technical solutions will be proposed in order to optimize the PV installation.

Seismic reinforcement of historical steel bridges in Japan

Both the Kiyosu and Eitai Bridges, registered as important cultural properties in 2007, are located in the lower reaches of the Sumida River in Tokyo. They were rebuilt in the latter half of the 1920s after the great Kanto earthquake of 1923 in the Japanese capital. By examining their anti-earthquake performance under the revised new standards based on the information obtained from the magnitude M7.3 great Hanshin Awaji earthquake of 1995, it was discovered that strengthening was required for both bridges. Strengthening design was considered and discussed from 2012 to 2014. It was concluded that with respect to the Kiyosu Bridge, the installation of dampers on both girder ends was required. With respect to the Eitai Bridge, the bearings on both piers were immobilised by placing additional horizontal bearings. Also, the addition of stiffeners to the arch ribs was deemed necessary to increase rigidity. The strengthening work was carried out from 2014 to 2015. This experience is expected to supply useful information for strengthening and repair/design work of historical bridges.

Launching of the San Cristobal Bridge

The San Cristobal Bridge in Chiapas, Mexico, is a three-span (71.5, 180, and 71.5 m) curved steel composite and orthotropic box girder erected by incremental launching. Lessons learned from the collapse during launching of the San Cristobal Bridge as well as the redesign and relaunching of the new bridge are discussed. After the collapse of the San Cristobal Bridge, T. Y. Lin International was hired by the new contractor, Ingenieros Civiles Asociados, to investigate the cause of the collapse of the original bridge, check the redesign of the bridge, and perform the erection engineering of the bridge. From the site investigation, it was concluded that the collapse of the structure was caused primarily by the failure of the shear studs and the consequent loss of composite action of the girder cross section over Pier 2. To ensure the safe erection of the structure, the redesign of the new bridge included the following changes: addition of shear studs, increase of deck posttensioning during launching, increase of the concrete slab strength, and addition of stiffeners to the bottom flange and webs. To match the predicted and measured deflections during launching, a calibration of the effective deck inertias (consistent with a 12 × tslab and contrary to the AASHTO specifications) was necessary to account for the effects of shear lag and the actual effective slab width.

A planar unimorph-based actuator with large vertical displacement capability. II. Theory

A piezoelectric actuator utilizing a planar trellis-like arrangement of multiple unimorph elements is described which produces displacements perpendicular to the plane of the actuator. The unimorph elements are connected in series mechanically so that the vertical displacement of each unimorph element in the structure adds to the vertical displacements of the other elements, resulting in a large overall vertical displacement at the output of the actuator. A simple electromechanical model of the actuator is developed. The model consists of a voltage-actuated force source, which is the result of the piezoelectric properties of the unimorph bars that make up the actuator, in parallel mechanically with a stiff spring that models the elastic response, both bending and twisting, of the unimorph elements. The long moment arms inherent in the geometry of the actuator make a substantial contribution to the overall compliance of the actuator. The addition of stiffeners to the actuator can significantly reduce the effect of these moment arms, and thus substantially increase the stiffness of the actuator. As a result, the force generation capability of the actuator is significantly increased without affecting its displacement capability.

Structural acoustics and vibration behavior of complex panels

Among the many mechanical parameters that influence structure-borne sound are the effects of stiffeners, added mass and complex support conditions along the structure boundaries. In the present paper, these effects are incorporated into a model of sound radiation in air from a complex, baffled, rectangular panel under harmonic point force or point moment excitation. A complex panel is thus defined as a panel which is stiffened lengthwise and widthwise by flexural-torsional beams, which carries point masses and which is elastically restrained against transverse displacement and rotation along the edges. The vibration of the panel assumes no fluid loading and is solved using the Rayleigh-Ritz method with simple polynomial trial functions. The expressions of the kinetic and strain energies associated with stiffeners, added mass and elastic boundary conditions, are detailed. A simple computation scheme is used to derive the farfield sound pressure from the transverse displacement of the panel. Numerical results are shown in terms of the mean quadratic velocity of the panel, radiated sound power and radiation efficiency for a variety of situations including force or moment excitation, simply-supported, clamped or free edges, addition of stiffeners and addition of a point mass, and are used to draw some useful guidelines in practice.

Dynamic and Static Axial Crushing of Axially Stiffened Square Tubes

The axial impact of thin-walled tubes with square cross-sections, which incorporate axial stiffeners, is studied in this paper. An examination is made into the influences of stiffener depth (T), number of stiffeners (N) and the effect of external or internal stiffening. The experimental results on mild steel specimens of side width c suggest, for a given impact energy, that the permanent axial displacements are not reduced significantly by the addition of stiffeners unless T/c exceeds a certain value.