Member Forces Research Articles

Effect of the CHS on Seismic Responses of the Single-Layer Spherical Reticulated Shell under Vertical Seismic Motions

Single-layer spherical reticulated shells are typical roof structures for the gymnasiums. The center-hung scoreboard (CHS) is large weight display device which is usually suspended on the roof of the gymnasium. The effect of the CHS on the dynamic characteristics and seismic responses of the single-layer spherical reticulated shell (SPRS) is not fully clear. In this paper, the effect of the CHS on the SPRS under vertical seismic action is investigated. Two kinds of FE models are built with Abaqus software, including the flexibly suspended model and the simplified model. In a simplified model, the CHS is simplified as four fixed masses on the four CHS suspension nodes. The dynamic explicit method is used for the seismic responses, and the Lanczos method is used for the dynamic characteristics. The influence of the CHS weight and the sling length of on dynamic characteristics and seismic responses are analysed. It turns out that in the flexibly suspended model, the first three vibration modes are free swing of the CHS, and the CHS weight and the sling length have a significant impact on the fourth and subsequent modes. The length of the sling has a large impact on some low-order frequencies, but has little impact on the high-order frequencies. Compared with the simplified model, the axial forces of some structural members and some nodal acceleration in the flexibly suspended model under vertical seismic motions would increase by as high as 523% and 564%, respectively. It turns out that the seismic responses of the SPRS would be underestimated if a simplified model is used for analysis. The region in the central of the SPRS, the hoop members of the SPRS, and the support platform are the most affected regions in terms of both axial force and nodal acceleration.

Exploring NATO’s enlargements in Northern Europe: Theorizing military transformation

This article seeks to theorize the transformation of the armed forces in Northern Europe by examining its drivers during previous NATO enlargements in the region. The exploration includes the German reunification in 1990, the Polish entry in 1999, and the joining of the three Baltic States, i.e., Estonia, Latvia, and Lithuania, in 2004. Based on these experiences, the article identifies some theoretical considerations for transformation in conjunction with the current accession process of Finland and Sweden. Based on a realist logic, we conclude that the ongoing transformation should be underpinned by a new operational design, hence considering the need for flexibility and for managing potential new expeditionary shocks. To this end, we argue that the focus must initially be internally within the Alliance, i.e., to proceed with novel operational planning for northern Europe before turning the attention to the transformation of the armed forces of the new members.

Effect of the MHS on Earthquake Response of Space Truss Structures under Horizontal Earthquake Motion

Space truss structures are commonly used in long-span roof structures. Recently, middle-hung scoreboards (MHS), a kind of large-scale display device flexibly suspended in the center of the roof, have been widely used in gymnasiums. However, the effect of the MHS on dynamic characteristics and earthquake response of space truss structures needs to be investigated. In this paper, the effect on the MHS under horizontal earthquake motion is studied. The simplified model, where the MHS is simplified to four fixed masses on a structure, and the flexibly suspended model are established with Abaqus software, and the earthquake response is analyzed by the time-history method with the dynamic explicit method. The influence laws of the wire extent and the MHS weight are discussed. Compared with the simplified model, the nodal acceleration and the axial force rise up to 2.123 times and 1.575 times, respectively, in the flexibly suspended model, indicating that the amplification effect of the MHS acts significantly under horizontal earthquake motion. It turns out that the earthquake response of a space truss structure could be underestimated if a simplified model is used. The crest acceleration of both top chord nodes and bottom chords nodes are greatly influenced by the MHS weight but little affected by the wire extent. The influence laws of the MHS weight and the wire extent on crest axial forces of structural members are very complicated. The central regions of both the top chords and the bottom chords are the most affected regions, and the boundary regions parallel to the direction of the earthquake motion are the least affected regions. It is suggested that the envelope value under the conditions of different wire extent and MHS weight are used for structural design.

Perbandingan Hasil Analisa Perhitungan Rangka Kuda-Kuda Kayu Dengan Menggunakan SAP-2000 dan Metode Titik Buhul

This research is a study that discusses the comparison of the results of the analysis of the calculation of the forces on the wooden framework using the Structure Analysis Program-2000 (SAP-2000) and method of joint. The value of each force of vertical bars, horizontal bars, tensile bars, and compression members at each point of the wooden framework will be calculated on three wooden framework spans with spans of 7m, 9m, and 11m. Comparison of the results of the calculation of the value of the rod force from the two methods will be compared to see the efficiency of the calculation analysis of the two methods. From the results of the calculation of the method of joint and the Analysis of Structure Analysis Program-2000 (SAP-2000) in calculating and analyzing the value of each vertical bar force, horizontal bar, tension member, and compression member, the difference between each rod force is at (0- 0.51) kg. This shows that the calculation analysis using the Structure Analysis Program-2000 (SAP-2000) is faster and more efficient in calculating each bar force.

Numerical analysis on the seismic performance of subway station in ground crack area

The site soil with ground cracks would cause strong motion and large deformation under major earthquakes, which brings a serious threat to underground structures. However, the ground crack effect on the seismic response of underground structures was unclear. This study developed a series of numerical analyses to study the seismic performance and damage mechanism of a rectangular-section subway station located in a ground crack area. After verification of the developed model, the structural responses of the subway stations in different sites subject to different earthquakes were evaluated in terms of acceleration response, inter-story drift, and damage pattern. Furthermore, a parameter analysis was performed to address the effects of structural position in the site, structural overburden depth and dynamic shear modulus of soils on the seismic performance of the subway station in the ground crack area. The results showed that the presence of ground crack exacerbated the shear deformation of the site soil and increased the internal forces of the lateral members, resulting in substantial damage to the subway station. The subway station in the ground crack area had poorer seismic performance than the station in the uncracked area, especially for station crossing the ground crack. Particularly, the ground crack effect on the seismic performance of subway stations should be carefully considered in the design of shallow-buried underground structures in soft soils.

On the Seismic Performance of the Single-Layer Reticulated Shell with a Center-Hung Scoreboard under Multiple Seismic Excitations

Single-layer reticulated shells are widely used as roof structures of gymnasiums. However, the seismic performance of the single-layer reticulated shell with a center-hung scoreboard (CHS), which is a kind of large-scale display device suspended on the roof center of many gymnasiums, has not been fully studied. In this paper, the influence of the CHS on the seismic response of single-layer reticulated shells is investigated. Single-layer reticulated shells and the CHS-integrated models including flexibly suspended models and simplified models are established, respectively, using the Abaqus software. The responses of integrated models are calculated by an explicit dynamic method under 3D seismic action. The axial forces of the flexibly suspended case and the simplified case where the scoreboard is simplified as fixed masses on the roof structure are compared. Compared with those in the simplified model, the axial forces of some shell members and some nodal acceleration in the flexibly suspended model under multiple seismic excitations would increase by as high as 125% and 315%, respectively. It turns out that seismic responses of the single-layer reticulated shell would be underestimated if a simplified model was used for seismic response analysis. The region near the boundary and the region neighbouring the support platform members are the most affected regions due to the combination of the horizontal swing effect and the vertical impact effect of the CHS under multiple seismic excitations.

CONSTRUCTION STAGE ANALYSIS OF SEGMENTAL BOX GIRDER BRIDGE

Segmental bridge construction is very common in Pakistan. However, the impact ofstructural system changes before and after the completion of segmental bridge construction is achallenge and major concern for construction stakeholders. Therefore, in this study, construction stageanalysis was performed for balanced cantilever construction technique to check the safety andserviceability of the bridge. Through time dependent analysis, considering the construction sequenceand creep deformation of concrete, structural responses related to the member forces were reviewed.Moment reversal was observed in the cantilever segments near the face of the pier. Therefore,maximum compressive and tensile stresses were observed in the top and bottom fibers of the girder,respectively. These stresses were within the AASHTO LRFD limits for construction stage loads.Results demonstrated that the creep moment redistribution started when the structural system changedfrom statically determinate to indeterminate stage. Furthermore, it was concluded that the timedependent deformation of concrete was the governing factor in order to achieve the final designmoments.

“A Day of Blood and Valor”: terrorism and social tensions in 1970s Israel

ABSTRACT On June 13, 1974, four Palestinian militants penetrated kibbutz Shamir in northern Israel, killing three women before being killed by an ad-hoc force of kibbutz members. The attack on Shamir generated a new discourse in Israel about civilian reaction to terrorism and the concept of the citizen-soldier. But this discourse was intertwined with contemporaneous social and ethnic conflicts, as it included comparisons between the events in Shamir and in other communities struck by Palestinian terrorism around the same period. Analyzing the public reactions to the raids on Shamir and other Israeli communities – mainly the towns of Kiryat Shmona and Ma’alot – this article argues that, in contrast to received opinion, security threats did not serve as a social glue keeping together a divided Israeli society, but rather accentuated ethnic and social tensions plaguing Israel in the 1970s.

Integrating a focus on health equity in implementation science: Case examples from the national cancer institute's implementation science in cancer control centers (ISC3) network.

A Health Equity Task Force (HETF) of members from seven Centers funded by the National Cancer Institute's (NCI) Implementation Science in Cancer Control Centers (ISC3) network sought to identify case examples of how Centers were applying a focus on health equity in implementation science to inform future research and capacity-building efforts. HETF members at each ISC3 collected information on how health equity was conceptualized, operationalized, and addressed in initial research and capacity-building efforts across the seven ISC3 Centers funded in 2019-2020. Each Center completed a questionnaire assessing five health equity domains central to implementation science (e.g., community engagement; implementation science theories, models, and frameworks (TMFs); and engaging underrepresented scholars). Data generated illustrative examples from these five domains. Centers reported a range of approaches focusing on health equity in implementation research and capacity-building efforts, including (1) engaging diverse community partners/settings in making decisions about research priorities and projects; (2) applying health equity within a single TMF applied across projects or various TMFs used in specific projects; (3) evaluating health equity in operationalizing and measuring health and implementation outcomes; (4) building capacity for health equity-focused implementation science among trainees, early career scholars, and partnering organizations; and (5) leveraging varying levels of institutional resources and efforts to engage, include, and support underrepresented scholars. Examples of approaches to integrating health equity across the ISC3 network can inform other investigators and centers' efforts to build capacity and infrastructure to support growth and expansion of health equity-focused implementation science.

COMPLEMENTARY ENERGY PRINCIPLE FOR CABLE NETWORKS IN TERMS OF FORCE VECTOR VARIABLE

An alternative approach to the variation formulation of static equilibrium problem for cable networks is proposed. The dual minimization principle is derived in terms of force variables. The full vector force in the cable member is chosen as the dual variable. Unlike the previously proposed treatments of the problem using the scalar axial force variable the elastic energy retains the most general form until the closing steps. It is only assumed to be a convex function of the member end-to-end vector. As a result the nonsmooth asymmetric response of the cable does not appear in the form of inequality in the very beginning. Instead it shows up in the final form of the complementary energy functional, which turn out to be non-differentiable for zero member forces. The kinematic relations between member elongations and nodal displacements convert into the force equilibrium conditions in terms of nodal reactions and member force vectors. The Dirichlet boundary conditions appear in the dual form as a linear term in the complementary energy functional. For the linear elastic cables this approach lead to a second-order cone optimization problem with two sets conical constraints. Such formulation provides flexibility and thus can be potentially extended to account for phenomena such as inter-fiber friction and adhesion. Keywords: complementary energy, variational principles, cable networks

Nonlinear technique of prestressing spatial structures

One of the crucial aspects of the design of structural space systems is the degree of prestressing since it is involved in the load transferring, deformability and charges. The prestress state can be reached via required member alteration. This paper presents an efficient nonlinear numerical approach based on the force method for prestressing the spatial nonlinear structures to the desired level through computing nonlinear actuation as a function of external nodal displacements. Two equations are derived for indicating the required amount of member alteration eo and prestressing level by using Taylor's series and Pade approximation methods. This technique can be applied to both rigid and flexible spatial structures. The present technique is validated based on three numerical examples, and the computational findings are in well agreement with the compared methods. The results show that the new approach requires less effort and makes greater economic sense. Moreover, the member forces with concern to nonlinear eo of double-layer space grid structure by imposing lack of fit of some members successfully obtained.

Effect of Soil-Pile-Structure Interaction on Behaviour of Offshore Jacket Structure

Offshore jacket structures are generally supported on pile foundations. Studies have evaluated the effect of soil-pile interaction on design of foundation; however, effect of soil-pile-structure interaction on behaviour of jacket structure has received little attention. Hence, present study focuses on understanding the influence of soil conditions, soil-pile interaction and foundation modeling approach on deformation characteristics and member forces of jacket structure. Linear static analysis on a typical 4-legged battered jacket structure is performed using STAAD Pro., subjected to dead/live loads and environmental loads. The water depth of 120 m and wave heights of 5 m, 10 m and 15 m are considered for this study. Morison’s equation considering Stokes 5th order wave theory is used for calculation of wave forces on jacket structure. The supports are modelled as skirted pile groups. The piles are represented by springs, with stiffness calculated using soil-pile interaction analysis. The soil conditions used in the study are varied for different compaction states of sand and different consistency states of clay and various parameters such as lateral/vertical deflection, support reactions, forces in leg, beams and bracings have been compared. It is concluded that ignoring soil-pile-structure interaction during analysis of jacket structure would underestimate the lateral/vertical deflections, support reactions, shear force and bending moment for leg, and axial forces in beam and plan bracing of the structure. No substantial impact of the interaction on other member forces is observed. Jacket structure founded on clayey soil exhibits higher deformation and member forces as compared to sand in general. The study is expected to help structural engineers in adopting an appropriate modelling approach, considering soil-pile-structure interaction, to obtain more realistic response for jacket structures.

A Parametric Study on Effect of Wave Height, Water Depth and Support Conditions on Behaviour of Offshore Jacket Structure

Fixed offshore jacket structures are constructed for facilitating oil/gas exploration and production. These structures and their foundations are designed to resist large vertical and lateral loads. Various factors including water depth, wave height and support conditions would affect the response of jacket structures. However, few studies have focused on understanding the response of offshore jacket structure due to variation in these factors. In this context, the present work evaluates response of typical X-braced, square base, 4-legged battered jacket structure using STAAD Pro. under combined vertical and lateral environmental loading. The variables included are water depth (60 m, 90 m and 120 m), wave height (5 m, 10 m and 15 m) and two foundation modelling approaches (viz., fixed at pile location and with defined pile stiffness). The connection between structure leg and pile location is modelled to simulate realistic connection. Deck loads, wind forces and current velocities are considered constant for this study. The wind and wave loads have been applied in parallel, perpendicular and diagonal directions with respect to jacket structure. The wave forces are calculated by Morrison’s equation. For obtaining pile stiffness, medium dense sand layer is considered as foundation soil. The increase in water depth and wave height results in corresponding linear increase in lateral deflection and support reactions, the effect of water depth being more prominent. Moreover, lateral and vertical deflection, shear force and bending moment in the legs, the axial forces in the lower tie beams and plan bracings, and support moments are observed to increase when pile locations are modelled with appropriate vertical, lateral and rotational stiffness instead of fixed support. The effect of water depth on member forces is higher as compared to wave height. The present work deliberates on the mechanisms/reasons to explain the observed results and contributes in direction of framing decision matrix for design optimization of jacket structures.

Experimental and Finite Element-Based Investigation on Lateral Behaviors of a Novel Hybrid Monopile

A monopile is the most conventional structure foundation for offshore wind turbines (OWTs) in the world. However, the Korean offshore wind industry has mostly been using the jacket type of foundation. The main reason for the current situation in Korea is that most of the marine soil consists of weak layers of sand and clay. Thus, the monopile foundation depth has to be deep enough to satisfy the intended serviceability design requirement of the monopile and the rotation limit at the seabed; a conventional monopile design concept alone might be insufficient in Korean offshore conditions, or otherwise could be very expensive, e.g., resulting in a rock socket installation at the tip of the monopile. The main objective of this paper is to introduce a novel hybrid monopile that is composed of a monopile and a supplemental support with three buckets, followed by assessing the lateral resistance of the hybrid system through physical experiments and finite element (FE) simulations. Namely, 1/64.5 small-scaled monopile and hybrid physical models with a monopile diameter of 7 m for a 5.5 MW OWT were loaded monotonically. The results show that the hybrid monopile improves the lateral bearing capacity regarding the initial lateral stiffness and ultimate load. The FE analyses of the corresponding physical models were also implemented to support the results from the physical model test. The numerical results, such as the structural member forces and soil deformation, were analyzed in detail. Additionally, a case study using FE analysis was conducted for the 5.5 MW OWT hybrid monopile support installed in a representative Korean weak soil area. The results show that the hybrid monopile foundation has a larger lateral resistance and stiffness than the monopile.

Heuristic Optimization of a New Type of Prestressed Arched Truss.

This paper represents new approaches for calculating, designing, and optimizing prestressed arched trusses with a tie member. Structural systems with long spans, such as trusses, beams, frames, etc., are subjected to a considerable/substantial risk of losing load-carrying capacity because of the different types of loads used. Some traditional design methods define the values of prestressing force in the tie member and internal forces in the truss elements to avoid this load capacity loss. However, the accuracy and limits of the determination of the forces are not necessarily known. The authors offer a new type of prestressed arched truss and some new approaches in the design and calculation process to solve these disadvantages. The study's main objectives were to design an innovative and new geometric form of prestressed arched truss, which allows the development of high-value prestressing force, to optimize a new truss for reducing self-weight, increasing load-carrying capacity compared to its analogs. The force, stiffness matrix, and simulated annealing methods were used during the study. A new advance to the optimization of prestressed arched truss suggested by the authors reduces the self-weight and improves the load capacity of the truss by 8-17%, depending on the span.

Shaking table tests and numerical modeling of discontinuous suspended ceiling system with free boundary condition

As one type of vital nonstructural component, the suspended ceiling (SC) system is widely used in public buildings but was severely damaged in past earthquakes. This study comparatively investigates the seismic behaviors of two typical SC systems, one of which is a single-layer suspended ceiling (SLSC), and the other is a double-layer suspended ceiling (DLSC). Full-scale shaking table tests are conducted on two ceiling specimens with free boundary condition. The damage patterns and earthquake responses in terms of acceleration, displacement, strain, and axial force of grid members are analyzed and compared. Experimental results show that the pounding behavior at the ceiling perimeter has significant effects on the seismic behavior of SC. The peripheral grid members and main-cross tee connections are most vulnerable to earthquakes. With the accumulated damage in SC, the final collapse of both specimens occurs suddenly. Additionally, the connections between the threaded rods and grid members significantly affect the seismic behavior of SC. Compared with the specimen DLSC, the specimen SLSC exhibits much better seismic performance. Lastly, the simplified numerical models of both specimens are established. The numerical simulation results agree well with the experimental results.

Response Spectrum Analysis of a RC Building Based on Complete Quadratic Combination (CQC) Method

In the realm of structural design, Seismic Analysis is crucial. Many structures have collapsed because of earthquakes; as a result of numerous studies, different methods for analysing and determining vibration modes of a structure have been created. Seismic analysis can be done in two ways: static analysis and dynamic analysis. The basic mode of vibration dominates the response in the static technique of seismic analysis, and the mass and stiffness of the structures are evenly distributed, resulting in a regular shape, however this assumption fails for irregular buildings. As a result, dynamic methods are used to solve this issue. Response spectrum is one such dynamic method that is relatively simple to utilize compared to others. The benefit of employing the seismic response spectrum method is that it aids in the prediction of displacement and member forces in structural systems. As a result, this method aids in determining peak structural responses within a linear range, which can then be used to calculate lateral forces created in structures due to earthquakes, allowing for more earthquake-resistant building design. Although this method is approximate, it is a cost-effective and beneficial method for preliminary design research. The response spectrum method is used on STAAD.PRO V8i software to design a G+4 residential structure in our study. The building’s measurements are 16 meters long, 12 meters wide and 15 meters tall. The foundation was built to a depth of 1.5 meters. The structure was built to withstand earthquakes in seismic zone III on medium-density soil. Dead load (IS 875 Part I), Live load (IS 875 Part II), Seismic Load (IS 1893 Part I), and Wind Load are some of the load instances that were presented based on Indian Standard code (IS 875 Part III). To acquire the best response, the response spectrum modal combination Complete Quadratic Combination (CQC) is used. Various parameters like wind intensity, seismic parameters, dynamic weight, modal participation factors, base shear and peak storey shear are calculated. Base shear and peak storey shear are found to maximum in Mode 2 and between 5th and 6th respectively.

Numerical modeling and experimental validation for suspended ceiling system with free boundary condition

As one type of commonly used non-structural component in public buildings, suspended ceilings (SCs) may suffer severe damage or even collapse under earthquakes. However, convincing numerical simulation on the SC is scarce due to its strongly nonlinear behavior. A refined numerical model for SC with free boundary condition is developed based on a full-scale shaking table test in this study. Grid connections, between main tees, main tee and cross tee, and cross tee and sub cross tee, are the main source of strong nonlinearity in SC. Their hysteretic models are built according to the cyclic loading tests first. The nonlinear impact and friction behavior at the ceiling perimeter are also considered. By conducting time history analysis of SC, the simulated responses of acceleration, displacement, and axial force of grid members are analyzed and compared with shaking table test results. The comparison results demonstrate that the proposed model is capable of predicting the seismic responses of the SC. Lastly, parametric analysis is conducted to investigate the influence of the width of peripheral gap, the length and diameter of threaded rods, and the thickness of panels on the seismic performance of SC. Outcome of this study is beneficial for modeling and seismic design of SC system.

Analytical solution for quick decision of tied–arch bridge parameters at early-design stage based on Hellinger–Reissner variational method

The tied-arch bridge is the combined system of an arch, a beam and suspenders. There have been a few methods applied in the design stage of the analysis of tied-arch bridges including finite element analysis and approximate solutions. The approximate solution based on the Ritz method has been very popular in the analysis of hybrid bridges during the early design stages for its high efficiency. The disadvantage of the Ritz method is that it only directly determines the deformation values while the forces in the structural members should be decided through the obtained deformation values, which highly decreases the accuracy of the force values. Based on the Ritz method, the Hellinger–Reissner (H–R) variational principle is introduced here to improve the approximate solution. It analyzes both the deformation and forces of the tie-arch bridge directly. This is the first time of the application of this method in the analysis of the tied-arch bridges. The advantage of the H–R variational principle is that it provides the forces and deformation values independently and directly which highly enhances the accuracy of the results. For verification, the material properties of the tied-arch bridge of the second-stage project of Line No.1 in Wuhan railway transportation are applied here. And the results from H–R variational method show good agreement with finite element analysis. Hence, the presented method could be a relatively good alternative to use in the early-design stage of the tied-arch bridges.

Using Explainable Artificial Intelligence to Identify Key Characteristics of Deep Poverty for Each Household

The first task for eradicating poverty is accurate poverty identification. Deep poverty identification is conducive to investing resources to help deeply poor populations achieve prosperity, one of the most challenging tasks in poverty eradication. This study constructs a deep poverty identification model utilizing explainable artificial intelligence (XAI) to identify deeply poor households based on the data of 23,307 poor households in rural areas in China. For comparison, a logistic regression-based model and an income-based model are developed as well. We found that our XAI-based model achieves a higher identification performance in terms of the area under the ROC curve than both the logistic regression-based model and the income-based model. For each rural household, the odds of being identified as deeply poor are obtained. Additionally, multidimensional household characteristics associated with deep poverty are specified and ranked for each poor household, while ordinary feature ranking methods can only provide ranking results for poor households as a whole. Taking all poor households into consideration, we found that common important characteristics that can be used to identify deeply poor households include household income, disability, village attributes, lack of funds, labor force, disease, and number of household members, which are validated by mutual information analysis. In conclusion, our XAI-based model can be used to identify deep poverty and specify key household characteristics associated with deep poverty for individual households, facilitating the development of new targeted poverty reduction strategies.