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Cross-linkable poly(arylene ether nitrile)s containing side propenyl groups (DPEN) were synthesized through nucleophilic aromatic substitution polymerization from biphenol, 2,2′-diallylbisphenol A (DBA), and 2,6-dichlorobenzonitrile. The structures of resultant copolymers were characterized by Fourier transform infrared and proton nuclear magnetic resonance spectroscopies. The properties of copolymers were investigated by thermal (differential scanning calorimetry and thermogravimetric analysis) analysis, inherent viscosity measurements, and mechanical tests. The results showed that allyl groups rearranged into propenyl groups during the polymerization. The copolymers with increasing content of DBA had high glass transition temperatures ranging from 207°C to 169°C and good thermal and thermo-oxidative stability with the 5 wt% loss temperatures in the range of 511–423°C under nitrogen and 471–402°C in air atmospheres, respectively. They also exhibited good mechanical property with tensile strength of 105–79 MPa. Meanwhile, the cross-linking reaction was studied through heat treatment. The result showed that the properties of DPEN containing side propenyl groups changed obviously after heat treatment, due to the fact that the double bond of PEN can be readily cross-linked to form net-shape polymers at high temperature. [ABSTRACT FROM AUTHOR]

To investigate the variability of ground motion characteristics (GMC) with the angle of seismic incidence (ASI) and the impact of seismic incident directionality on structural responses, first, a large-scale database of recorded ground motions was used to analyze the causes of GMC variability due to the seismic incident directionality effect (SIDE). Then a single-mass bi-degree-of-freedom system (SM-BDOF-S) with different types of symmetrical sections was selected to explore the influence mechanism of SIDE on the seismic responses. The results illustrated that the GMC has substantial variability with the ASI, which is independent of the earthquake source, propagation distance, and site condition, and exhibits complex random characteristics. Additionally, a classification method for ground motions is proposed based on this GMC variability to establish a criterion for selecting ground motions in seismic analysis considering the SIDE. Moreover, for an SM-BDOF-S, the response spectral plane is proposed to explain the transition behavior of spectral responses that are very similar among different stiffness ratios, but divergent for different types of ground motions. The influence of SIDE on structures is determined by their stiffness and stiffness ratio in the x - and y -directions, as well as the type of ground motion. [ABSTRACT FROM AUTHOR]

• We investigate a bipedal inverted pendulum (BIP) model for human–structure interaction. • Model comparison is carried out to show the effect of leg damping on BIP's gaits. • Measured and simulated ground reaction forces are compared in both time and frequency domains. • The ability of the proposed model to cover gait diversity is verified. The bipedal inverted pendulum with damping has been adopted to simulate human–structure interaction recently. However, the lack of analysis and verification has provided motivation for further investigation. Leg damping and energy compensation strategy are required for the bipedal inverted pendulum to regulate gait patterns on vibrating structures. In this paper, the Hunt–Crossley model is adopted to get zeros contact force at touch down, while energy compensation is achieved by adjusting the stiffness and rest length of the legs. The damped bipedal inverted pendulum can achieve stable periodic gait with a lower energy input and flatter attack angle so that more gaits are available, compared to the template, referred to as spring-load inverted pendulum. The measured and simulated vertical ground reaction force-time histories are in good agreement. In addition, the dynamic load factors are also within a reasonable range. Parametric analysis shows that the damped bipedal inverted pendulum can achieve stable gaits of 1.6 to 2.4 Hz with a reasonable first harmonic dynamic load factor, which covers the normal walking step frequency. The proposed model in this paper can be applied to human–structure interaction analysis. [ABSTRACT FROM AUTHOR]

Unbalanced snow loads on roofs have been a turbulent and significant problem for the building industry. Gables are one of the most common roof shapes, which are widely adopted as the roof shape for family residences, factories, ware houses, and garages. Series of experiments on an isolated gable-roof with or without scuttles and different roof pitches were done for the purpose of exploring the unbalanced patterns of snow loads. The model buildings made of wood have the same floor space, 2000 × 2000 mm but different roof pitches. A new open air snow–wind combined experimental facility was adopted in the experiments. The facility, which is like an open air wind tunnel with a snowfall simulator, can produce a stable wind field and snowfall environment for a specific duration. Artificial snow was used in the experiments, and particles properties were compared with natural snow previously proposed by the other authors. The experiment results indicated that the unbalanced snow loads were strongly connected with various wind velocities and roof pitches and a scuttle or other salient on the roof would bring an evident influence of patterns of snow distribution on the roofs. [ABSTRACT FROM AUTHOR]

Reciprocal grid structure is a structural system consisting of mutually supporting bars. Its geometry should satisfy not only the demands of architectural intents but also the requirements of the lapping relationship of the bars. Thus, form generation is the key problem in its design. Inspired by the physical building process of a reciprocal grid structure, self‐adaptive form generation method is proposed. In this method, an initial plane grid with the topology of required structural configuration is created first. Next, elements are iteratively lapped to realize a self‐adaptive generation of structural form. Two new parameters, bar lapping factor and rotation angle, are proposed to describe reciprocal grid structures quantitatively and make the form generation process easy. The efficiency and accuracy of the method are illustrated by comparisons with other form generation methods. Numerical examples demonstrate the applicability of the proposed method in the complex and realistic reciprocal grid structures. [ABSTRACT FROM AUTHOR]

Highlights • Based on four static loading experiments, a finite element simulation method of reticulated shell with roofing system is established; roofing system improve buckling load and plastic development, purlin is the main component in roofing system bearing static load together with the reticulated shell, the roofing panels play a relatively minor role. • The effect of roofing system tends to decrease when the span of reticulated shell increases. • The roofing system has a more significantly effect on the shell with larger initial geometric imperfections. Abstract The static stability of a single-layer reticulated shell has been systematically studied, but nearly all scholars have neglected the effect of the roofing system, and the simplified analytical method may lead to deviations between finite element analysis and the actual situation. In this paper, four full-scale reticulated shell substructure models with a roofing system were experimentally investigated to verify the effect of the roofing system. The finite element analysis (FEA) were established based on the experimental models, the connections between the purlin and purlin hanger were modelled as semi-rigid joints, the profiled sheets were modelled as equivalent orthotropic flat panels, and a weakened area was established to model the connection between the purlin and the roof panel. A series of finite element analysis models (FEM) of full-scale reticulated shells with roofing systems were established, and the effect of the roofing system on the full-scale reticulated shells' static stability was analysed. [ABSTRACT FROM AUTHOR]

Abstract A general forming method for super-long span mega-latticed structures has been developed, based on the key parameters for five types of structure, together with a finite element model. The method combines the molding idea for universal spherical mega-latticed structures and the geometric topological relations of the improved traditional single-layer reticulated shell. The static and economic indexes of six kinds of 800 m span mega-latticed structures, with the same geometry, control parameters and loads, were calculated, and the force law for these structures under static load identified. Then structures suitable for spans of 1000 m and 1200 m were considered. The static performance and economic indexes showed that the mechanical and economic performance of the Geodesic type mega-latticed structure and the Three-dimensional grid type mega-latticed structure were excellent. In order to promote the engineering application of these structures, the influence of four key parameters on the performance of 1000 m structures was studied, and a reasonable range of indicative parameters obtained. Highlights • It is proved that the modeling method is universal for spherical mega-latticed structures. • The paper can better explain the static properties and the stability of super-long mega-latticed structures. • It is proved that the structure types selected have good mechanical properties and economic performance. • It is proved that through the method of parameter analysis, economic and reasonable structures can be obtained. [ABSTRACT FROM AUTHOR]

Abstract: Free‐form grid structure is a kind of structure whose shape cannot be expressed by analytical functions. Although this kind of structure has been widely used in practice, how to generate the structural shapes that not only satisfy architectural requirements but also have excellent mechanical properties is still a problem. This article focuses on the shape generation of complex grid structures and proposes a novel shape‐generation method for free‐form grid structures. The method integrates numerical inverse hanging method and multiobjective optimization. First, it uses numerical inverse hanging method to generate structural shapes in low bending moment level. Next, it uses dynamic weight multiobjective firefly optimization algorithm to adjust the parameters of the inverse hanging method adaptively so that the structural shape can satisfy architectural requirements. Comparisons with former shape‐generation methods show that the proposed method is more effective. Numerical examples based on real structures illustrate the applicability of the proposed method in practice. [ABSTRACT FROM AUTHOR]

In previous studies, snowdrifts around different buildings have been investigated in wind or water tunnels, or in the outdoor environment, to ensure proper accessibility and the safety of structures. The pattern of snowdrifts is strongly connected to the speed and incidence angle of the wind. Two sets of experiments have been undertaken to investigate the influence of wind on snowdrift accumulation around a model and another set of experiments have been undertaken to explore the influence on two separated models. The building model is a wooden cube with dimensions of 0.5 × 0.5 × 0.5 m. The experiments are carried out in an open air snow-wind combined experimental facility, which is situated outdoors, like an open air wind tunnel with a snowfall simulator. The facility can produce a stable wind field and snowfall environment for a specific duration. During the experiments, environmental conditions, like temperature and humidity were measured on a PC-4 automatic weather station. The snow used in the experiments came from the natural snowfall on 01/19/2016-01/22/2016. After each experiment, the snowdrift geometry was measured by surveying approximately 300 points around the model. The results reveal that the patterns of snow distribution show a close relationship with the surrounding wind field of buildings. [ABSTRACT FROM AUTHOR]

The temperature effect often significantly affects the performance of large-span spatial structure and even becomes one of the controlling loads. To obtain the non-uniform temperature field distribution of the thin-walled steel members under solar radiation and the influence rules of various factors, in this paper, experimental studies are carried out with three groups of specimens including rectangular steel tube, I-shaped steel and circular steel tube. Based on the test data, the non-uniform temperature field distributions considering the influence of solar radiation intensity, member size and surface coating are analyzed in detail. Then, numerical methods for the temperature field of steel members are studied considering multiple environmental factors. The validity of the numerical method is evaluated with test results. Finally, based on the parametrical studies of the major influence factors, a simplified calculation approach is presented for practical engineering applications. The experimental study demonstrates that the non-uniform temperature distribution of steel members truly exists and cannot be overlooked. The numerical method for the temperature field in this paper is effective, and the simplified calculation approach can meet the required engineering precision. The research methods and conclusions of this work can provide valuable references for thermal design, monitoring and control of steel structures. [ABSTRACT FROM AUTHOR]

A comparison was made of the static behavior of a double-layer reticulated shell, a local triple-layered reticulated shell, a ribbed type mega-latticed structure and a Kiewitt type mega-latticed structure with the same geometrical parameters and loads. The results show that the Kiewitt type mega-latticed structure has the best structural performance. Then a complex structural configuration was analyzed in detail, using CAD 3D modeling, and a command-flow was developed to create the new structure automatically by ANSYS Parameter Design Language as an innovative structural-programming method. The static analysis and comprehensive stability analysis were conducted. The reasonable values of parameters for the overall buckling mode were summarized and the ultimate bearing capacity was accurately obtained by considering geometrical nonlinear, material nonlinear and initial curvature of the members. The nonlinear equilibrium paths were traced using the Arc-length method. Results indicate that the 800 m Kiewitt type mega-latticed structure has a very low sensitivity to geometrical nonlinear and a low sensitivity to initial curvature of members, but a high sensitivity to material nonlinear. Therefore, the Kiewitt type mega-latticed structure could be regarded as a reasonable super-large span structure with several advantages, including reasonable stresses, clear force transmission lines, economic steel consumption, high stiffness and good bearing capacity. [ABSTRACT FROM AUTHOR]

The unified wind pressure spectra model with certain precision can simplify the wind-induced response analysis and standardize the design process of the wind resistance. An auto-spectral model of wind pressure was proposed with three parameters which denote the descending slope, the dominant frequency and the peak value of the reduced auto-spectral curve respectively. The values of the model parameters were identified and studied statistically based on 4 types of rigid large-span roof models in which 115 typical wind tunnel pressures were measured. The results show that the distribution patterns of the parameters is in accord with the flow characteristics and can be expressed in the form of zone area, which may indicate the physical meaning of the parameters. The zone values of the parameters were summarized statistically, and the wind pressure spectral model was validated by 1) comparing the spectral curves with relevant studies and 2) comparing the wind-induced responses calculated through the proposed model with the wind tunnel data on 642 cases of large-span grid structures. It concludes that the spectral model can be applied in further exploring the wind load characteristics as well as calculating wind-induced responses in engineering practices. [ABSTRACT FROM AUTHOR]

The precise waterproofing mechanism for sodium silicate-based concrete sealers was experimentally explored using a Leeb hardness tester, a Fourier transform infrared spectroscopy, an X-ray diffraction microscopy, a thermal-gravimetric analysis, a surface area and porosity analyzer, a scanning electron microscope and an optical contact-measuring device. After treating the concrete surface with a sodium silicate-based concrete sealer, the new substance-sodium hydroxide-introduced into the concrete structure is undetectable most likely because of the quite low concentration and its migration to the concrete surface. The surface hardness of the concrete specimens impregnated with the sodium silicate-based concrete sealer is found to be increased by approximately 11.9% relative to the untreated concrete specimens. The content of the calcium hydroxide in the concrete structures decreases whereas the content of the calcium silicate hydrate (C–S–H gel) in the concrete structures increases compared with the untreated concrete structures. Sodium silicate-based concrete sealers are essentially surface hydrophilic agents, yet they do reduce the velocity of water ingress into the concrete structures, because the expansive and insoluble C–S–H gels partially fill the micro-pores, micro-voids and micro-cracks in the concrete structure to form smaller micro-pores, micro-voids and micro-cracks and improve the compactness and water impermeability of the concrete. [ABSTRACT FROM AUTHOR]

Most existing studies on single-layer spatial structures with semi-rigid joints were focused on spherical domes. The present paper analyzed the squared plan-form single-layer structures, examining the influence of joint-rigidity on the mechanical performances of the structures. An experiment has been conducted on a 5×6 m single-layer cylindrical reticulated shell with semi-rigid bolt-ball joints. The mechanical performance of the latticed shell is investigated in detail. Finite element analysis (FEA) model of the latticed shell is established taking material and geometric nonlinearities into account. The results show that the behavior determined using the FEA models correlates well with the experimentally observed behavior for the single-layer structures with semi-rigid joints. [ABSTRACT FROM AUTHOR]

Unbalanced snow distribution is one of the main reasons for the collapse of multi-span arch roofs due to excessive snow loads in the valley and leeward areas. The formation of uneven snowdrifts is closely related to the shape of the building as it seriously affects the turbulent structure and snow drifting process. This study aims to investigate the snowdrift characteristics of multi-span arch roofs based on a multiphase snowdrift approach. Firstly, the prediction accuracy of the flow field is tested to select a reasonable turbulence model. Then, the reliability of this multiphase approach is validated by comparing the results with a wind tunnel experiment of snowdrifts on a multi-span arch roof. The result preliminarily proves that this approach could well reproduce the unbalanced snowdrift on each span roof and at the trough. The snowdrift characteristics of multi-span arch roofs are investigated under different rise/span ratio and span number conditions based on the validated approach. The formation mechanism and characteristics of snowdrifts on different roofs are clarified by analysis. Finally, several typical distribution patterns are derived based on the statistical analysis of results. It is found that the middle-span roof bears a larger snow load than the roofs at both ends. • The paper proposes a multiphase approach that could accurately predict the snowdrifts on arch roofs. • The multiphase approach could well reproduce the snow drifting process and the sliding effect at roof edge. • Two kinds of unbalanced triangular snow loads are formed on the single-span arch roof according to the rise/span ratio. • The stacking snow load at the trough of the multi-span roof is about twice the peak snow load of the single-span roof. • The middle-span arch roof bears a larger snow load than the roofs at both ends of the multi-span building. [ABSTRACT FROM AUTHOR]

This study aims to provide a multiphase approach that could better consider the snow drifting development on a building roof and then apply it to the investigation of the snowdrift development on a long-span spherical roof. Firstly, the CFD prediction accuracy for the flow field and the snowdrift on a two-level step building is examined by comparing simulated results with that of a field measurement. The windward snowdrift caused by building's blocking effect and trajectories of snow particles under the action of aerodynamic force and gravity are both well reproduced by incorporating an additional source term and a slip term into the transport equations. Secondly, the prediction accuracy of the snowdrift formed on a spherical roof is confirmed through the comparison with a wind tunnel test. The snow slipping effect at the edge of the roof is also well reproduced by considering the angle of repose of the snow. Based the validated approach, the snowdrift characteristics on a long-span spherical roof are investigated under different inflow velocity conditions. Three kinds of distribution patterns, i.e., the full-span balanced distribution, half-span unbalanced distribution and transitional distribution between them, are observed. Furthermore, the predicted results correspond well with the resultant design codes developed by ISO 4355. Finally, the size effect of the building roof on snowdrifts is explored by simulating the snowdrift on the spherical roofs with different spans. It is found that the spherical roof would have to bear a larger snow load with the increasing roof span, namely, the long-span spherical roof has more risks due to the adverse snow load. • The paper proposes a multiphase approach that could accurately predict the snowdrifts on long-span roofs. • The multiphase approach could well reproduce the motion of snow and the non-equilibrium drifting process. • Three typical snow distribution patterns on the spherical roof and their corresponding inflow velocities are specified. • The long-span spherical roof is more likely to experience the most adverse snow loads. [ABSTRACT FROM AUTHOR]

Inclined suspended cables (ISCs) have several applications in the transmission lines of power network systems. This study attempts to simplify the modeling of ISCs by addressing their static and dynamic stiffness. The dynamic problem of a uniform damping ISC under a harmonic excitation is studied under the assumptions that the suspended cable is deflected in a parabolic profile during static equilibrium and all the displacements in the dynamic in-plane motion are small. A closed expression for the frequency response function (FRF) is derived, based on which the static stiffness of the ISC is established; this aids in modifying the Ernst's formula. Furthermore, the cable dynamic coefficient is defined by considering the participation factors and the minimum number of vibration modes. The dynamic stiffness of the ISC is established by combining the static stiffness and cable dynamic coefficient. In addition, a shaking table test of a reduced-scale tower-line system model is performed to verify the correctness of the finite element model of the suspended cable. The results of the static and dynamic analyses indicate that the spring model based on the dynamic stiffness, showing a good precision, has a higher computational efficiency compared with the suspended cable model. Finally, the spring model, which is applied to the tower-line system by choosing different seismic excitations, inclinations, sag-to-span ratios, and spans of ISCs, is valid for an arbitrary angle of inclination ranging between 0° and 50°. Moreover, its results are in very good agreement with those of the suspended cable model. Unlabelled Image • The dynamic characteristics of an inclined suspended cable (ISC) is studied. • The dynamic stiffness is determined based on the mode-superposition method. • The geometric, material, dynamic and damping features of ISCs are considered. • The spring model based on dynamic stiffness is validated by test and FEM. [ABSTRACT FROM AUTHOR]

Joints transfer forces propped by members to other sections of space frame. It support and connect braces with other members which provide restraints to members. In general, joints behavior is ideally rigid or ideally pinned (flexible) in typical design and study of space frames; ideally rigid Joints cannot undergo rotation and ideally pinned joints cannot transfer moment. In reality, rigid joints have relative flexibility which makes them rotate and ideally pinned have means to transfer moments. Thus, real space frame both idealized models are not real and all joints present a semi-rigid behavior [1,2]. Thus, real joint in space frame is "semi-rigid". Several tests have plainly shown that joints behave nonlinear because of gradual yielding of joint parts such as; plates, angles, bolts. Space frame buildings use bolted joints. However, joint behavior is complex to analyze because of discontinuities in joints areas. Features which influence joints behavior includes; bolts positions and spacing, bolts pretension and material properties. Other features such as; joints parts and contact areas evolution, compression center positions and stiffeners presence can change joints behavior. Tests can predict joints behavior, as well as elaborated modeling and analytical approaches. Space frames joints work under axial force, shear force, and bending moment. However, for most joints, axial and shear deformations are usually small liken to bending deformation [2]. This work considers only joints rotational deformation because of bending action. The present paper includes design of Aluminum bolted joints and explores it behavior experimentally. Also it analyzes and models the moment-rotation behavior of these joints by using Finite Element Model and mathematical formulas. Which will finally help to integrate the moment-rotation curves efficiently into a Space frame analysis computer program. • Aluminium joints mechanical performancesunder static loading. • Aluminium semi-rigid joints behavior. • Aluminium semi-rigid joints Numerical study. • Aluminiumsemi-rigid jointsmathematical predictionmodel. [ABSTRACT FROM AUTHOR]