Effect Of Gravity Load Research Articles

Simplification of KDS 14 Design Method for Slab–Column Connections Subjected to Unbalanced Moment

The current KDS 14 design method yields reasonable accuracy with acceptable safety in assessing the unbalanced moment-carrying capacity of slab–column connections. However, the model requires considerable computational effort owing to the effects of various design parameters, particularly the gravity-load effect. This study proposes a method to simplify the KDS 14 model to evaluate the unbalanced moment-carrying capacity of slab–column connections. In the proposed method, the gravity-load effect is decoupled from equations used for evaluating unbalanced moment-carrying capacity components. Subsequently, the total unbalanced moment-carrying capacity is determined by establishing an interaction between the gravity shear ratio and unbalanced moment components without considering the gravity-load effect. For practical design purposes, final simplified design equations are proposed. The reliability of the simplified method is validated based on a comparison with the current KDS 14 design code using a comprehensive database encompassing interior, exterior, and corner slab–column connections. Furthermore, a parametric study based on the proposed simplified approach, current design codes, combined with finite-element (FE) analysis is performed to elucidate the effects of constituents on the unbalanced moment-carrying capacity of corner slab–column connections. The results show that the proposed simplified model and KDS design method are strongly correlated with the experimental and FE results for a range of design parameters. Meanwhile, the ACI 318 model consistently provides a lower limit for strength prediction, thus yielding overly conservative and safe results compared with the test and FE results in most cases.

Post-buckling behavior of variable-arc-length elastica pipe conveying fluid including effects of self-weight and pressure variation

This paper investigated the post-buckling behaviors of a variable-arc-length (VAL) elastica pipe caused by internal transporting fluid motion, accounting for the effects of the self-weight and variation of internal fluid pressure. Both weak-form and strong-form formulations of the VAL elastica pipe were developed. The weak-form formulation was derived by the virtual work principle, and later solved using the nonlinear finite element method (FEM). The strong-form formulation was derived using equilibrium of the force and moment equations, the geometrical relationship of the differential pipe segment, and the energy conservation of the transported fluid. Because of the large displacement analysis, the variation in the internal pressure inside the pipe was considered, which was taken into account by energy conservation based on the Bernoulli principle. Then, the set of nonlinear governing first-order differential equations, corresponding to the two-point boundary value problem, was conveniently solved using the shooting optimization method (SOM). The numerical results obtained from the presented FEM and SOM analyses independently verified each other, with good agreement between these two methods. The parametric study considered the effects of gravity load (pipe and fluid self-weights) and internal fluid pressure on the post-buckling characteristics of the VAL pipe. The numerical results showed that without the pipe and internal fluid weights, the transporting fluid exerted an axial compressive force on the pipe, causing post-buckling phenomena. Beyond the critical state, the support rotation and the length of the VAL pipe increased as the internal fluid velocity decreased. Finally, by including the effect of self-weight, the mode exchange of the odd buckling modes (1st and 3rd modes) was found from the load-displacement path.

Analysis of the causes determining dimensional and geometrical errors in 316L and 17-4PH stainless steel parts fabricated by metal binder jetting

This work aims at investigating the causes affecting the dimensional and geometrical accuracy of holes in metal binder jetting stainless steel parts. Parallelepiped samples with a through hole were produced using AISI 316L and 17-4PH powders, differing for diameter (3, 4, 5 mm), and position of the axes with respect to the building plane (6, 9, 12 mm distance). Dimensions and geometrical characteristics were measured at green and sintered state by a coordinate measuring machine, determining the dimensional change and the geometrical characteristics. As expected, the shrinkage of linear dimensions is anisotropic; moreover, change in volume and sintered density are significantly affected by the position in the printing chamber. Higher shrinkage was measured along building direction (Z) – 18.5 ÷ 19.5%, than in the building plane – 16.5 ÷ 17.5%, and slightly higher shrinkage – 0.5 ÷ 0.8% was measured along powder spreading direction (X) than binder injection direction (Y). A variation up to 3% in relative density of sintered parts depending on the position in the building plane was observed in 316L. The dimensional change of diameters generally confirmed the shrinkage predicted by the model previously developed—difference between real and expected dimensional changes lower than 3%, except for three geometries (4 ÷ 6%). The cylindricity form error of sintered parts was strongly underestimated by the prediction model (up to 0.15 mm), but underestimation was considerably reduced (generally lower than 0.05 mm) adding the cylindricity form error due to printing. Dimensional and geometrical accuracy of holes are strongly affected by shape distortion of the parallelepiped geometry, in turn due to layer shifting and inhomogeneous green density during printing, and to the effect of frictional forces with trays during sintering. Gravity load effect was also observed on the holes closest to the building plane. Future work will improve the reliability of the prediction model implementing the results of the present work.

Finite Element Modeling and Analysis of Perforated Steel Members under Blast Loading

Perforated steel members (PSMs) are now frequently used in building construction due to their beneficial features, including their proven blast-resistance abilities. To safeguard against structural failures from explosions and terrorist threats, perforated steel beams (PSBs) and perforated steel columns (PSCs) offer a viable alternative to traditional steel members. This is attributed to their impressive energy absorption potential, a result of their combined high strength and ductile behavior. In this study, numerical examinations of damage assessment under the combined effects of gravity and blast loads are carried out to mimic real-world scenarios of external explosions close to steel structures. The damage assessment for PSBs and PSCs considers not just the initial deformation from the blast, but also takes into account the residual capacities to formulate dependable damage metrics post-explosion. Comprehensive explicit finite element (FE) analyses are performed with the LSDYNA software. The FE model, when compared against test results, aligns well across all resistance phases, from bending and softening to tension membrane regions. This validated numerical model offers a viable alternative to laboratory experiments for predicting the dynamic resistance of PSBs and PSCs. Moreover, it is advisable to use fully integrated solid elements, featuring eight integration points on the element surface, in the FE models for accurate predictions of PSBs’ and PSCs’ behavior under blast loading. A parametric study is presented to investigate the effect of web-opening shapes, retrofitting, and different blast scenarios. The results obtained from the analytical FE approaches are used to obtain the ductile responses of PSMs, and are considered an important key in comparisons among the studied cases.

Estimation of Shallow Landslide Susceptibility Incorporating the Impacts of Vegetation on Slope Stability

This study aimed to develop a physical-based approach for predicting the spatial likelihood of shallow landslides at the regional scale in a transition zone with extreme topography. Shallow landslide susceptibility study in an area with diverse vegetation types as well as distinctive geographic factors (such as steep terrain, fractured rocks, and joints) that dominate the occurrence of shallow landslides is challenging. This article presents a novel methodology for comprehensively assessing shallow landslide susceptibility, taking into account both the positive and negative impacts of plants. This includes considering the positive effects of vegetation canopy interception and plant root reinforcement, as well as the negative effects of plant gravity loading and preferential flow of root systems. This approach was applied to simulate the regional-scale shallow landslide susceptibility in the Dadu River Basin, a transition zone with rapidly changing terrain, uplifting from the Sichuan Plain to the Qinghai–Tibet Plateau. The research findings suggest that: (1) The proposed methodology is effective and capable of assessing shallow landslide susceptibility in the study area; (2) the proposed model performs better than the traditional pseudo-static analysis method (TPSA) model, with 9.93% higher accuracy and 5.59% higher area under the curve; and (3) when the ratio of vegetation weight loads to unstable soil mass weight is high, an increase in vegetation biomass tends to be advantageous for slope stability. The study also mapped the spatial distribution of shallow landslide susceptibility in the study area, which can be used in disaster prevention, mitigation, and risk management.

Old masonary tower analysis visual inspection, NDT, and macro-modeling

A comprehensive analysis was conducted on a 106-year-old masonry tower to assess its response to gravitational forces and wind effects. Various techniques, including visual inspection, non-destructive testing, and finite element analysis (FEA), were employed in this study. Visual inspection played a vital role in evaluating the Tower’s exterior and interior components, aiming to detect signs of damage or wear at any level and comparing them to the analyzed model. Dimensioned and assembled drawings were utilized to create a detailed 3D finite element model, employing the Ansys Workbench's macro and homogeneous modeling techniques. Non-destructive testing was carried out on multiple structural parts of the tower, using techniques, such as the rebound hammer and ultrasonic pulse velocity tests, to gather the mechanical properties of the stone and brick masonry. These properties were incorporated into the finite element model to evaluate the Tower's structural responses during analysis. The tower's structural response under gravitational forces was determined using standard code regulations and guidelines, and stress and strain responses were compared to the actual structural morphology observed during the inspection. The highest stress was found in the stone elements between the connection of the dome and the drum on the second floor. Furthermore, the tower’s response to wind, including stress and deformation, was thoroughly examined at the same location, revealing the maximum response under gravity loading. This study pinpointed critical and weak areas that require retrofitting and strengthening using modern techniques to safeguard these monumental historical structures for future generations. The combined use of visual inspection, non-destructive testing, and finite element analysis proved to be an effective approach in assessing the response of the 106-year-old masonry tower to gravity loading and wind effects.

Application of direct analysis method on the long span steel structures

Along with development of the method for calculating the stability of steel structures, the direct analysis method is one of the recommended methods. This method is adopted by many design codes including AISC 360 and SNI 1729:2020. The direct analysis method has been considered as the primary method since it can overcome the limitations of the previous method, known as the effective length method. The main objective of this study is to understand the application of the direct analysis method on the long span steel structures. This research considers the effect of building height, earthquake loads, and gravity loads on the steel structure stability. The results show that the direct analysis method is a simpler and more efficient method since it has taken into account the second-order effect and has a smaller stress ratio value compared to the Effective Length Method. Therefore, the direct analysis method can be used as a recommendation method for calculating the stability of steel structures.

Breaking law of overlying strata in shallow coal seam fire area under thermal–mechanical coupling effect

AbstractThe cracks formed by the breaking and collapse of the overlying strata are the oxygen supply channels for the continuous combustion of coal fires. The development of cracks is of great significance for determining the scope of the fire area and controlling the fire efficiently and accurately. To study the development law of cracks, a breaking model of the overlying strata in the shallow coal seam fire area is established on the basis of beam theory considering the coupling effect of gravity load and temperature field. The physical model of the coal fire is established based on the similarity principle. The temperature data from rock strata in the model are monitored by the infrared thermal imager. The dynamic distribution function of the roof temperature field is obtained by fitting. According to the breaking model theory, the position of the maximum tensile stress on the roof of the shallow fire area is the middle of the lower surface. The theoretical calculation value of the first breaking distance of the roof is 0.575 m, which is consistent with the experimental results of the physical model. The maximum tensile stress of the roof under the thermal‐mechanical coupling is slightly less than that under the load only. For shallow coal seams, the thermal stress generated by the coal fire increases the first breaking distance of the roof.

Lateral behavior and PFI model of sinusoidal corrugated steel plate shear walls

This study focused on the lateral behavior of sinusoidal corrugated steel plate shear walls (CoSPSWs), which consist of a steel boundary frame and sinusoidal corrugated infill wall plates. Firstly, eigenvalue buckling analyses were conducted on sinusoidal corrugated wall plates under pure shear, and local as well as global shear buckling stress formulas were proposed. Nonlinear pushover analyses were then conducted on sinusoidal corrugated steel plate shear walls with different corrugation configuration, corrugation direction as well as influences from gravity loads. The results show that the lateral behavior of sinusoidal corrugated wall plates is obviously affected by the corrugation configuration and gravity load effects, but not much by the corrugation direction. Based on the shear slenderness ratio, sinusoidal corrugated wall plates could be classified into stocky, moderate and slender walls, with lateral load-resisting mechanism corresponding to shear yielding, inelastic shear buckling, and elastic shear buckling followed by incomplete tension field action, respectively. CoSPSWs with stocky wall plates tend to have both good lateral capacity and ductility, CoSPSWs with moderate wall plates would still have good lateral capacity but lower ductility, and CoSPSWs with slender wall plates would have good ductility but lower lateral capacity. Shear strength formulas were proposed for horizontal corrugated wall plates, not affected by gravity loads due to accordion effects, as well as vertical corrugated wall plates considering the gravity load effects. Plate-frame interaction (PFI) models were also proposed for horizontal and vertical CoSPSWs considering the gravity load effects.

Experimental-numerical assessment of laterally-loaded CFS frames with steel sheathing and K-shaped braces

In this study, the behavior of cold-form steel (CFS) frames equipped with various configurations of steel sheathing, and K-shaped braces are experimentally investigated. Low lateral resistance is a major problem with the CFS shear walls. Despite their advantages, such as being lightweight, ease of fabrication, and an environmentally friendly system, their lack of adequate lateral strength prevents engineers from widely using them, especially in areas with medium to high seismicity or mid-rise buildings. In this regard, a total of seven full-scale specimens with different configurations of steel sheathing and k-braced, with and without cladding, were tested to investigate their seismic behavior. The effect of gravity loading on the lateral resistance of the CFS frames was tested using three specimens. The gravity loadings of the CFS specimens were determined assuming an ordinary two-story CFS frame building. The effect of different CFS frame configurations on the energy dissipation, secant stiffness, and ductility factor of those frames was evaluated. The failure modes observed in this study can be classified into brace connection failure, brace element failure, sheathing, and chord stud failure. Moreover, using a calibrated simplified nonlinear model, the seismic behavior of different CFS configurations under earthquake excitation was examined. Based on the obtained experimental and numerical results, it can be concluded that the proposed dual CFS frame and shear wall configuration has a better performance both in the cyclic test and the numerical studies compared to the CFS walls with steel sheathing or bracing alone.

Nonlinear seismic analysis of RC framed structures with horizontal and vertical base-isolation

The ratio of the vertical-to-horizontal peak ground accelerations highlights the fact that values greater than one tend to occur in the near-fault area, where the corresponding ratio of spectral accelerations may be amplified in the range of low vibration periods. The high vertical-to-horizontal stiffness of a base-isolation system (e.g. high-damping-rubber bearings, HDRBs) of a reinforced concrete (RC) framed structure causes the superstructure to behave like a fixed-base one in the vertical direction. Seismic damage induced by vertical excitation is generally located at the upper storeys, where the effects of gravity loads generally prevail over those of the horizontal loads and an amplification of the vertical motion is expected. In the present work, attention is focused on the combination of horizontal and vertical base-isolation resulting from the in-series vertical arrangement of a HDRB and a HDR layer, the latter not affecting the horizontal stiffness of the isolator but reducing its vertical stiffness. The main objective is to evaluate the isolation ratio in the vertical direction that needs to be considered for effective protection against significant vertical component of near-fault earthquakes. A five-storey RC framed structure is first designed as fixed-base in a medium-risk zone, in compliance with a former Italian seismic code. It is retrofitted by the insertion of a horizontal-vertical base-isolation system, with nominal, upper-bound, lower-bound and mixed design properties defined by current European seismic codes. Nonlinear seismic analysis of the test structures is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research Center database and scaled to match the design spectrum of acceleration. Finally, the vertical stiffness to be assigned to the isolation system to obtain a shift from the vibration periods of maximum amplification is evaluated by wavelet analysis, including the moving resonance effect induced by inelastic deformation of the superstructure.

Seismic ratcheting of eccentric gravity loaded moment‐resisting frame buildings

AbstractStructures may predominantly inelastically deform in a single direction during earthquakes and incur greater damage. This behavior is known as seismic ratcheting and can be caused by eccentric gravity loads. Code clauses were introduced in Canada and New Zealand to amplify displacements obtained from static analysis methods to consider seismic ratcheting effects. However, such clauses are based on analyses of reinforced concrete (RC) wall or single‐degree‐of‐freedom (SDOF) structures, and methods to mitigate seismic ratcheting behavior were not explicitly provided. In this study, parametric analyses of steel and RC moment resisting frame buildings were performed to evaluate the adequacy of code clauses, identify parameters which influence seismic ratcheting behavior, and propose methods to mitigate such behavior. It was found that the New Zealand code underestimated the displacement increase for RC buildings, though it was able to envelope the displacement increase for steel buildings while the Canadian code was conservative. Additionally, the displacement increase was found to be sensitive to the building's post‐yield behavior and ground motion properties. However, assumptions of these properties during design may not be reflective of the actual building and seismic conditions, indicating that a reliable estimate of the increase in displacement is difficult to obtain. Instead, employing mitigation measures to reduce seismic ratcheting effects, such as designing to higher seismic demands, adding a secondary structural system to increase the building's post‐elastic stiffness, or providing more balanced lateral strengths after adjusting for eccentric gravity load effects are better measures to counter seismic ratcheting effects caused by eccentric gravity loads.

A finite element study on the ultimate lateral drift capacity of interior reinforced concrete flat slab-column connections

Reinforced concrete (RC) flat slabs may be a part of the lateral load resisting system or may only serve as a gravity load bearing element in RC structures. In both cases, RC slab-column connections have a crucial role in the global seismic performance of RC buildings. Punching shear failure in flat slabs concentrated in the slab-column connection region is a common brittle failure mode which can adversely affect the global seismic behavior of structures. However, few studies have been done on the numerical simulation of brittle shear failure in slab-column connections under simultaneous gravity and lateral loads. In this paper, to evaluate the behavior of RC slab-column connections under simultaneous gravity and lateral loads and to examine the effects of various influential parameters on the lateral drift capacity of the connections, a numerical study is conducted on interior slab-column connections. The investigated influential variables are the flexural reinforcement in the slab, slab thickness, and the dimensions of the supporting column. The numerical study is implemented in the finite element software ABAQUS. First, the numerical model is verified through modeling three interior RC slab-column connections tested in other experimental studies. Then, all the connections are analyzed under the simultaneous effects of gravity and lateral loads and their lateral load-drift curves are determined. According to the analysis results, in addition to the gravity load intensity, other variables such as flexural reinforcement ratio, slab thickness, and the size of the supporting column affect the lateral behavior of the connection.

A comparative study on structural design alternatives for twisted tall buildings with outriggers

Tall buildings are seen as iconic landmarks because of their bold effect on the city silhouette. To control this bold effect in an aesthetically desired manner, designers search for intriguing forms such as twisted buildings. There are two main approaches for designing the structural system of a twisted tall building. In the first approach, the twisted form of the building is obtained only by the rotation of the floors, and the structural system is maintained in a conventional, perpendicular way. Alternatively, the structural system and the floors of the building twist together. This study designates these as non-adaptive and adaptive, respectively. With different heights and angles of twist, non-adaptive and adaptive tall building models are created and analysed under the combined effect of wind and gravity loads. The dynamic properties, drift, moment, and torsion demands are compared to scrutinize and assess the potentials and limitations of these alternative approaches.

Effect of slab gravity load on slab-column connection with different compressive strengths

Current design codes specify the effective compressive strength of a column-slab connection when columns and slabs have different concrete compressive strengths. However, this approach assumes that no gravity load is applied to the slab. The gravity loads acting on the slab weakens the confinement of the slab-column connection and reduces the effective compressive strength of the column. Therefore, the effective compressive strength of the column specified in the current design code can be considered unsafe when gravity loads act on the slab, similar to the case of an actual structure. In this paper, the existing studies on slab-column connection, in which the gravity loads act on the slab, were comprehensively reviewed, and an effective compressive strength of the column based on the strain in the top slab reinforcement was proposed. In addition, three slab-column connections were fabricated, where the gravity loads acting on the slab and constraint condition of the slab were set as test variables, and axial load tests were conducted.

Effective buckling length of frames with tapered columns and partially tapered beams

This paper presents stability analysis of steel frames composed of linearly tapered columns and partially tapered restraining beams. In the first part of the stability analysis, closed-form equations for the bending stiffness of the symmetrical and unsymmetrical partially tapered restraining beam are derived and presented in form of design charts. Subsequently, slope deflection equations of linearly tapered column subjected to axial compressive load are then assembled along with the bending stiffness equations of partially tapered beams to determine the elastic critical load and the effective buckling length factor for non-sway and sway steel frames. Numerical examples and efficient design charts are presented for several braced and unbraced steel frames. Moreover, the effect of gravity loads acting on leaning columns connected to sway frames is investigated. Based on this investigation it is concluded that correction of effective buckling length factor based on story buckling concept can be extended to cover steel frames with tapered column as well.

Evaluation of global ocean tide models based on tidal gravity observations in China

Previous studies show that the calculated loading effects from global ocean tide models do not match actual measurements of gravity attraction and loading effects in Southeast Asia. In this paper, taking advantage of a unique network of gravity tidal stations all over the Chinese mainland, we compare the observed and modeled tidal loading effects on the basis of the most recent global ocean tide models. The results show that the average efficiencies of the ocean tidal loading correction for O1, K1, M2 are 77%, 73% and 59%, respectively. The loading correction efficiencies using recent ocean tidal models are better than the 40 years old Schwiderskis model at coastal stations, but relative worse at stations far from ocean.

Shear strength of stiffened steel shear walls with considering the gravity load effect through a three-segment distribution

Former investigations have shown that the gravity load will significantly reduce the shear strength of the steel shear walls (SSW), especially in the case of a stocky wall that has high buckling stress under heavy compression load. However, only a few have been carried out on stiffened SSW, even though it has high compression buckling stress. The present study aims to narrow the knowledge gap by conducting a theoretical analysis and a numerical evaluation. The stiffened SSW is divided into several sub-walls by vertical and horizontal stiffeners. For each sub-wall, a three-segment vertical stress distribution under the gravity load is proposed. The tension field stress of inclination tension strips of each sub-wall, with considering the effect of the gravity load through the proposed three-segment vertical stress distribution, is determined through the Von Mises yield criterion. Shear strength of the wall is calculated as the sum of the shear strength of each sub-wall, while that of the boundary frame is determined according to a wall-frame model. To evaluate the proposed approach, an experimentally verified finite element model using the software ANSYS/LS-DYNA is developed. The results show that the proposed approach is able to accurately consider the gravity load effect of the stiffened SSWs of different stiffeners configurations.

Progressive collapse of 2D reinforced concrete structures under sudden column removal

Once a column in building is removed due to gas explosion, vehicle impact, terrorist attack, earthquake or any natural disaster, the loading supported by removed column transfers to neighboring structural elements. If these elements are unable to resist the supplementary loading, they continue to fail, which leads to progressive collapse of building. In this paper, an efficient strategy to model and simulate the progressive collapse of multi-story reinforced concrete structure under sudden column removal is presented. The strategy is subdivided into several connected steps including failure mechanism creation, MBS dynamic analysis and dynamic contact simulation, the latter is solved by using conserving/decaying scheme to handle the stiff nonlinear dynamic equations. The effect of gravity loads, structure-ground contact, and structure-structure contact are accounted for as well. The main novelty in this study consists in the introduction of failure function, and the proper manner to control the mechanism creation of a frame until its total failure. Moreover, this contribution pertains to a very thorough investigation of progressive collapse of the structure under sudden column removal. The proposed methodology is applied to a six-story frame, and many different progressive collapse scenarios are investigated. The results illustrate the efficiency of the proposed strategy.

Gravity Load Effect on Seismic Response of Glass Fiber- Reinforced Polymer-Reinforced Concrete Slab-Column Edge Connections

Gravity Load Effect on Seismic Response of Glass Fiber- Reinforced Polymer-Reinforced Concrete Slab-Column Edge Connections