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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]

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]

An investigation of the seismic behaviour and a design method for single-layer reticulated shells with semi-rigid joints is described in this paper. A semi-rigid joint system has some bending and rotational rigidity that lying between that of a rigid-joint and a pin-joint. The seismic capacity of Kiewit reticulated shells with bolt-ball joints is analyzed in detail on the basis of the bending rigidity of the bolt-ball joint reported by others. The change rules of natural frequency and seismic internal force coefficient are reviewed by analyzing of large-scale shells with different span, depth-to-span ratio, bending rigidity, roof load, section size of members and seismic wave parameters. The seismic internal force coefficient (under the influence of bending moment) for shells with a semi-rigid joint system is summarized statistically to provide the maximal seismic response envelop. [ABSTRACT FROM AUTHOR]

A new control method is proposed to improve the seismic performance of double-layered Kiewitt Spherical reticulated shells. The approach taken is to replace selected bars in the shell with passive viscoelastic dampers; thus, the grid of the shell doesn't need to be changed. Computational models of the shell with the eight different damper topologies are developed using ANSYS®. The seismic response of the shell is simulated to determine the performance of the various damper topologies. Aparameter study is conducted to determine optimal values for the damping coefficient of dampers. Finally, the dynamic stability and failure modes of the shell are investigated through incremental dynamic analysis. If designed well, failure of the controlled shell is usually the result of a strength failure, rather than a dynamic instability. [ABSTRACT FROM AUTHOR]