Experimental investigation on friction and squeezing of roof structure key blocks corner upon long-wall face

The coefficients of friction and squeezing of the key blocks comer in the roof structure of underground coalface are key factors to roof structure stability quantitative analysis. In this paper, through the special test of three-type corner friction and squeez- ing of real rock specimens, and physical simulation test on the roof key blocks of roof structure as well as the finite element calcula- tion of the corner stress distribution and failure mechanism, the characteristics of friction and squeezing of the roof key blocks comer are revealed. It is found that the friction angle of the roof key blocks corner is the residual friction angle, and the frictional angle of the roof key blocks is 22-32° (average 27°), so the friction coefficient is determined as 0.5. It also found the squeezing strength is less than the uniaxial strength, and the squeezing coefficient of the roof blocks corner is determined as 0.4. Based on the results, the ground control theory can be updated from qualitative analysis to quantitative analysis.

Proposal of Stainless Steel Roof Structure and Tiles for Gymnasiums

This work proposed an architectural alternative project of a stainless steel roof structure that uses roof tiles also in stainless steel with emphasis on roofs for multi-sport gymnasiums.In the development of the work,two existing multi-sports gymnasiums are taken as a reference,but with ASTM(American Society for Testing and Materials)A36 steel roof structure.The proposed cover system uses cables and light gauge profiles,in commercial stainless steel,which reduces the weight and of course the final price of the roof structure.A structure that presents technical feasibility is obtained and analyzed by checking its behavior with respect to the efforts and displacements generated by the combinations of the acting loads,following the safety recommendations of the applicable standard.It is verified that using the stainless steel structure proposed in this work would cost 42%of the reference structure if this were in AISI(American Iron and Steel Institute)304 stainless steel.And this cost tends to be minimized due to greater durability and consequent reduction in maintenance costs of this type of steel.

Software Practicalization for Analysis of Wind-Induced Vibrations of Large Span Roof Structures

Wind loads are key considerations in the structural design of large-span structures since wind loads can be more important than earthquake loads, especially for large flexible structures. The analysis of wind loads on large span roof structures (LSRS) requires large amounts of calculations. Due to the com- bined effects of horizontal and vertical winds, the wind-induced vibrations of LSRS are analyzed in this pa- per with the frequency domain method as the first application of method for the analysis of the wind re- sponse of LSRS. A program is developed to analyze the wind-induced vibrations due to a combination of wind vibration modes. The program, which predicts the wind vibration coefficient and the wind pressure act- ing on the LSRS, interfaces with other finite element software to facilitate analysis of wind loads in the de- sign of LSRS. The effectiveness and accuracy of the frequency domain method have been verified by nu- merical analyses of practical projects.

Analysis of solar radiation changes in Chinese solar greenhouses with different roof structures based on a solar radiation model

Chinese solar greenhouses(CSGs)are important agricultural production facilities.Under non-artificial heating conditions,solar radiation is the only CSGs energy source.It is highly important to optimally obtain solar energy in greenhouse construction and production.In this study,a solar radiation model for solar greenhouses was adopted to explore the quantities of solar radiation in greenhouses considering different front roof forms and angles.Herein,the solar radiation amounts corresponding to five roof forms,namely,double-section arc,parabolic,oval,arc,and linear roofs,are compared and analyzed during the four solar periods(beginning of spring,vernal equinox,beginning of winter,and winter solstice).It was found that the solar radiation of oval roof greenhouses on the ground was the largest and was 4.44%-23.68%higher than that of parabolic roofs.In addition,the cumulative sum of light on the linear roof greenhouse wall is also the largest and was 6.02%to 12.08%higher than the parabolic roof greenhouse in the four solar terms.Moreover,the solar radiation in CSGs was compared with front roof angles of 25°,30°,and 35°.It was observed that the solar radiation amount gradually increases with increasing angles.Notably,the variation at an angle of 35°influences the solar radiation of the paraboloidal CSGs ground and elliptical CSGs north wall to the greatest extent,which increased by 8.23%and 12.74%,respectively.This study confirms the role of front roof form and inclination angle in enhancing the greenhouse solar radiation level.

Slotted Hole Effect on Damage Mechanism of Gymnasium Building with RC Frame and Steel Roof

On the 2011 off the Pacific Coast of Tohoku Earthquake, gymnasium buildings exhibited the unexpected structural damages, which prevented a use as evacuation shelters in during- and post-disaster periods. The major failure occurring on the connection between the RC column top and steel roof as well as the cracks in the RC column base was observed during the emergent inspection. According to the earlier studies, it was implied that the presence of the slotted hole possibly deteriorates the seismic capacity;however, the length of slotted hole was fixed at a certain value. Facing this concern, this research attempts to clarify the influence of the slotted hole length through a comprehensive parametric study by pushover and seismic response analyses. In conclusion, it has been discovered that the slotted hole deteriorates the seismic capacity for the connection failure up to almost 50% of that without slotted hole. Moreover, the discrepancy of characteristics obtained by the static and dynamic analyses is originated by means of the presence of slotted hole. This slotted hole effect should be noted by structural engineers and researchers to provide the adequate seismic diagnosis and strengthening.

Using of Key Stratum Theory to Study the Structural Development of Roof Aquifer

During the underground mining of coal resources,overlying rocks on the roof of excavated tunnels will be destroyed due to ground pressure,and as a result,part of them will break and fall into the tunnels.How to determine the distribution of fractured areas and fissures presents a major problem for preserving the overlying aquifer.

Basic Structural Forms of Main Roof

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Comparison of large deformation failure control method in a deep gob-side roadway: A theoretical analysis and field investigation

Under the dual influence of the mining disturbance of the previous working face and the advanced mining of the working face,the roadway is prone to large deformation,failure,and rockburst.Roadway stabilization has always significantly influenced deep mining safety.In this article we used the research background of the large deformation failure roadway of Fa-er Coal Mine in Guizhou Province of China to propose two control methods:bolt-cable-mesh+concrete blocks+directional energy-gathering blasting(BCM-CBDE method)and 1st Generation-Negative Poisson’s Ratio(1G NPR)cable+directional energy-gathering blasting+dynamic pressure stage support(πgirder+single hydraulic prop+retractable U steel)(NPR-DEDP method).Meantime,we compared the validity of the large deformation failure control method in a deep gob-side roadway based on theoretical analysis,numerical simulations,and field experiments.The results show that directional energy-gathering blasting can weaken the pressure acting on the concrete blocks.However,the vertical stress of the surrounding rock of the roadway is still concentrated in the entity coal side and the concrete blocks,showing a’bimodal’distribution.BCM-CBDE method cannot effectively control the stability of the roadway.NPR-DEDP method removed the concrete blocks.It shows using the 1G NPR cable with periodic slipping-sticking characteristics can adapt to repeated mining disturbances.The peak value of the vertical stress of the roadway is reduced and transferred to the deep part of the surrounding rock mass,which promotes the collapse of the gangue in the goaf and fills the goaf.The pressure of the roadway roof is reduced,and the gob-side roadway is fundamentally protected.Meantime,the dynamic pressure stage support method withπgirder+single hydraulic prop+retractable U steel as the core effectively protects the roadway from dynamic pressure impact when the main roof is periodically broken.After the on-site implementation of NPR-DEDP method,the deformation of the roadway is reduced by more than 45%,and the deformation rate is reduced by more than 50%.

Introspection on improper seismic retrofit of Basilica Santa Maria di Collemaggio after 2009 Italian earthquake

The 2009 L’Aquila, Italy earthquake highlighted the seismic vulnerability of historic masonry building structures due to improper ＂strengthening＂ retrofit work that has been done in the last 50 years. Italian seismic standards recommend the use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete （RC） or steel elements, inserting RC tie-beams in the masonry and new RC floors, and using RC jacketing on the shear walls. The L’Aquila earthquake revealed the numerous limitations of these interventions, because they led to increased seismic forces （due to greater additional weight） and to deformation incompatibilities of the incorporated elements with the existing masonry walls. This paper provides a discussion of technical issues pertaining to the seismic retrofit of the Santa Maria di Collemaggio Basilica and in particular, the limitations of the last （2000） retrofit intervention. Considerable damage was caused to the church because of questionable actions and incorrect and improper technical choices.

Structural design and thermal performance simulation of shade roof of double-slope greenhouse for mushroom-vegetable cultivation

A new type of roof structure was developed for the shade room in a double-slope greenhouse used for mushroom-vegetable planting.A simulation model was developed to evaluate the thermal performance of the new roof with an insulation thickness of 0.12 m in Beijing,China.The results showed that(1)the indoor air temperature of the shade room with the newly implemented shade roof was 2.7℃-4.9℃ higher than that of an ordinary shade room during the winter months;(2)The indoor air temperature of the solar room adjacent to the shade room with the new roof was higher than that of the ordinary solar room and the minimum indoor air temperature of the solar room was increased 1.9℃ at winter night;(3)the indoor temperature of the shade room with the new roof design was 2℃-4℃ lower than that of the ordinary shade room during the summer months;(4)Under factory production conditions,which were conducted in a controlled environment to promote the annual growth of the edible fungus,the heating energy consumption of the shade room after the implementation of the new roof structure was reduced by 69.3%,the amounted to total energy savings of 61.3% per year.The new roof structure provided a significant improvement in the thermal environment compared to an ordinary shade room,improved the vegetable growth in the winter,and also significantly reduced the energy consumption and production costs.