Roof Load Research Articles

Prediction of the height of destressed zone above the mined panel roof in longwall coal mining

Abstract Longwall mining is one of the most widely used underground mining methods most suitable in relatively flat-lying, thick, and uniform coalbeds. Due to extraction of the coal seam, the panel roof strata above the mined zone will be destressed and then the roof loads will be redistributed and transferred to the front abutment and neighboring solid sections with higher load bearing capacity where the adjacent access tunnels and the corresponding barrier pillars are located. The height of destressed zone (HDZ), in this paper is taken as equivalent to the combined height of the caving and fracturing zones above the mined panel roof induced due to longwall mining. The height of destressed zone plays a vital role in accurate determination of the amount of loads being transferred towards front abutment and panel sides. The paper describes the mechanism of development of the height of this zone. Finally, five new simple, yet conclusive, mathematical approaches to estimate the height of destressed zone are presented. The results of the methods proposed are compared with each other and with the comparable methods. The methods proposed are further compared and verified with in-situ measurements reported in the literatures. The comparative results confirm the agreement that exist among the methods and those with the in-situ measurements as well. Finally the methods have shown that, in short term, the height of destressed zone ranges from 6.5 to 24 times the extraction coal seam height; while, in long term, the height of destressed zone ranges from 11.5 to 46.5 times the extraction coal seam height. Therefore, beyond this height the overburden pressure will be transferred towards the front abutment, the adjacent access tunnels, the intervening barrier pillars as well as the panel rib-sides.

모임지붕형 쌍곡포물선 쉘구조의 유한요소해석

본 연구에서는 쉘의 테두리를 보가 둘러싸고 있는 전통적인 형태와 모서리보를 제거한 형태의 모임지붕형 쌍곡포물선쉘구조의 유한요소해석결과비교를 통해 모서리보의 역할을 확인하고, 또한 지붕의 경사도의 영향을 분석하였다. 유한요소해석에 의하면 쉘면에 작용하는 하중은 쉘 대각선 방향의 아치작용을 통해 모퉁이의 지점에 직접 전달되므로 막이론에 비해 테두리보에는 부재력이 작게 작용하고 모퉁이의 지점 부분의 쉘에는 응력이 증가되는 것으로 나타났다. 모서리보를 제거하면 지점 부근의 쉘에 더욱 응력이 집중되고 경사진 모서리 부분의 처짐이 증가하는데 이와 같은 현상은 지붕의 경사도가 낮아짐에 따라 현저해지는 것으로 나타났다. 따라서, 모임지붕형 쌍곡포물선쉘 구조에서는 지점 부분의 쉘두께를 보다 증가할 필요가 있으며 경사도가 낮은 쌍곡포물선쉘 구조의 모서리보 제거는 주의가 필요한 것으로 나타났다. In this study, mechanical role of edge beams in the gabled hyperbolic paraboloid shells was investigated through the comparisons of Finite element(FE) analysis results between the shells structures with and without edge beams. In addition, the effects of roof slope was studied. FE analysis showed that roof loads was directly transferred to the supports at corners by the arch action in the diagonal direction of the shells, thus, less member forces in the edge and ridge beams but higher stresses near supports were estimated than those from the membrane theory. When the edge beams were removed, stress concentration in the shells near the supports and the deflections along the shell edge were increased. Such phenomenon were intensified as the roof slope decrease. Thus, in gable hyperbolic paraboloid shell, the thickness of the shell near supports needs to be increased and careful investigation should be made in the cases when the roof height is low and/or the edge beams are removed.

Virtual testing for the assessment of a double-sided roof crush based on the newly updated Federal Motor Vehicle Safety Standard 216

The newly updated Federal Motor Vehicle Safety Standard 216 enhances the requirements of the roof crush behaviour as it particularly focuses on the double-sided test protocol. This test will be mandatory from the year 2012 and will replace the single-sided test. The research presented herein aims at investigating the behaviour of a small European vehicle subjected to this newly updated Federal Motor Vehicle Safety Standard 216 and at assessing the effect of the variation in the loading combination of the pitch angle and the roll angle on the roof crush strength to quantify the difference in the performances. A Ford Fiesta FE model developed at the University of Bolton was refined and validated against the roof crush test. Thereafter a full factorial method was employed to the design of the experiment based on varying the pitch angle and the roll angle. The response functions concerning the resistance force of the double-sided roof were hence constructed with the results from a series of virtual tests based on nine levels of the roll angle and four levels of the pitch angle. Parametric studies were then conducted with respect to the effects of the body structural components, the windscreen and the variations in the roll angle and the pitch angle on the roof strength. The results show that the roll angle and the pitch angle are functions of the roof strength. In general, the roof on the near side performs in a stronger way than the roof on the far side and greatly influences the overall collapse behaviour. Within a crush distance of 127 mm (5 in), the strengths on both sides of the roof decrease as the roll angle varies from 10° to 45°. The variation in the pitch angle influences the resistance force. In addition, the windscreen is found to contribute significantly to the roof strength on the far side, hence demonstrating a strength which is artificially high, not quantifiable and not observed in real-world rollover crashes. From the virtual parametric analysis carried out, it shows once again that the recommended loading-angle combinations in the newly updated Federal Motor Vehicle Safety Standard 216 roof crush test should be a roll angle of 45° (and not 25°) and a pitch angle of 10° (and not 5°) for both near-side and far-side roof load application.

Uplift Capacity of Polyurea-Coated Light-Frame Rafter to Top Plate Connections

AbstractThis paper demonstrates the potential for using field-applied structural coatings to reinforce traditional framing members and standard building ties, thereby providing an improved and continuous foundation to roof load pathway. Tension tests were performed on light-frame rafter to top plate connections, some of which were reinforced with a hurricane tie, to establish how much of a difference a polyurea coating made as the joints between the stud and top plate, and top plate and rafter, were loaded to failure. The tests indicate that polyurea provides universal strengthening compared with hurricane ties with the added advantage that members and joints can be protected from a multitude of threats, including corrosion attributable to moisture, damage attributable to flood; and, with self-extinguishing properties fire. The addition of the coatings allowed both unreinforced and reinforced configurations to withstand higher loads (200–400% more). In general, the polyurea delayed the onset of failure an...

Impact of Vehicle add-ons on Energy Consumption and Greenhouse Gas Emissions

The primary objective of this study is to determine the impact of vehicle add-ons on energy consumption and greenhouse gas emissions (mainly CO2) for commonly used fossil fuels in passenger car. Various commonly used vehicle add-ons (police siren, advertising sign, taxi sign and roof rack) and roof load (e.g., ladder and barrel) produce additional aerodynamic drag. To measure the aerodynamic drag produced by these add-ons a wind tunnel study was undertaken using a replica reduced scale model passenger car. The aerodynamic drag for different add-on configurations were measured for a range of vehicle operating speeds and yaw angles. The results show that the vehicle add-ons have notable impact on aerodynamic drag as they can generate 5% to 40% more aerodynamic drag depending on cross wind effects. The taxi sign has minimum impact and the advertising sign has highest impact on aerodynamic drag. Also roof load such as ladder and barrel can significantly increase the drag. The aerodynamic drag was related to a range of commonly used fuels e.g., petrol, diesel, compressed natural gas (CNG) and liquefying petroleum gas (LPG) consumption, and their relative CO2 gas emissions. The results indicate that for a given range, the emission of CO2 is the highest for the CNG due to its lowest energy density.

Evaluation of Friction Properties According to Normal Force and Direction of Wood Grain in Real Contact Area

In Korea, there has been a traditional post and beam wood construction with large roof load. Because a large friction is generated in wooden joint or members, it is important to evaluate the friction between wood members according to wood direction. Because most of studies have been concerned with friction between wood and steel, excluding effect of real area of contact, there are a few studies on the friction between wood members. The object of this study was to evaluate friction or coefficient of friction accord- ing to normal force and real area of contact of wood. With Japanese larch (Larix kaempferi) test speci- mens, five steps of normal force and combinations of test were prepared. Results indicated that normal force had almost no affection on the friction, however there was difference about friction or coefficient of friction according to real contact conditions of wood grain and contact area.

Multi-Object Resonant Response Equivalent Static Wind Load of Large-Span Roofs

According to the strain energy equivalent, the resonant response equivalent static wind load of large span roof is derived. It solves the matter that should consider numerous structural response control objects on calculating equivalent static wind load for large span roofs, and establishes relationship with the structural strain energy introduced by fluctuant wind loads. Finally, the method is used to resonant equivalent static wind load analysis of 2008 Beijing Olympic Tennis Center Stadium roof structure. The results illustrate that the method proposed in this paper is effective and the precision is reliable.

Background Response Equivalent Static Wind Load of Large-Span Roofs Based on Energy Equation

Based on strain energy equivalent, the background response equivalent static wind load of large span roof is derived. It solves the matter that should consider numerous structural response control objects on calculating equivalent static wind load of large span roofs, and establishes relationship with the structural strain energy introduced by fluctuant wind loads. Finally, the method is used to background equivalent static wind load analysis of China National Stadium roof structure. The results illustrate that the method proposed in this paper is effective and the precision is reliable.

한국과 중국의 옥상녹화 제도 비교연구

This study focused on the regulations and support system of green rooftop landscaping between Korea and China. Our research found out regulations and support system to review the supplement point to understand the present state of green rooftop landscaping in the two countries. We aimed to provide basic legal information for the development of green rooftop landscaping regulations. Also, a management plan guide and after-evaluation guide were suggested. First, roof load safety is the foremost factor for the structure of green rooftop landscaping. It includes not only considering the weight of construction materials, but also accurately calculating weight of rain, snow and the rooftop`s capacity for people when the rooftop is designed. Second, the appropriate waterproof and root material should be selected basing on climatic conditions. Third, a maintenance and management plan needs to be established to regularly check the plant, facilities, soil and to maintain them. Fourth, the criteria of quality inspection are waterproof and root resistant material, and the growth and development of plants. Waterproof and root resistant materials are a very important part of rooftop greening, so they must be strictly inspected after construction. Fifth, the support system of rooftop greening should be continuously improved. The choice of the object and the amount of support should be strictly stipulated so that the construction of rooftop is promoted when volunteers do rooftop greening.

Cusp Catastrophe Models and Instability Mechanism of Underground Cavern’S Roof

The underground caverns were divided into underground spherical cavity and underground tunnel. From bean-slab theory and energy principle, the catastrophe models of underground spherical cavity and tunnel were built and the necessary and sufficient condition of roof failure was derived. Taken the cavern roof of Wenfu phosphate mine for example, the minimum thickness of roof was derived. The analysis of spherical cavity shows that the roof fails more easily when the roof thickness is smaller, the elastic modulus is smaller, the Poisson's ratio is smaller and the roof span and loads are bigger. The analysis of tunnel roof shows that the stability of tunnel roof is closely related to the vertical load and the horizontal load. In order to guarantee the roof stability, the observation of load acted on roof should be reinforced and some control measures should be taken according to the necessary and sufficient condition of roof failure.

Development of roof trusses with metal plate connectors using domestic plantation timber.

Metal plate connectors (MPCs) were developed and applied to truss assemblies to evaluate the structural performance of Japanese cedar roof trusses in the study. An MPC with a tooth length of 9 mm, a plate thickness of 0.9 mm, and a tooth density of 1 tooth cm^(-2) was designed and produced using SS33 structural steel sheets. The loading capacities of the designed MPC were 216~265 N per tooth, and the derived allowable lateral resistance was 68.3~86.4 N per tooth for Japanese cedar lumber joints in tension. Ultimate bending capacities and stiffness of the 38×140-mm wood roof truss system were 82.6 and 48.9% higher than those of 38×89-mm wood roof truss, respectively. No significant difference was found between Howe and Fink trusses. The critical failures in Japanese cedar roof trusses were located at the heel joint, and these accounted for 75% due to a combination of tooth withdrawal and plate failure in the 38×140-mm truss, and 87.5% due to the tooth withdrawal in the 38×89-mm truss. Flexural deflections of Japanese cedar roof trusses measured at the design load level were within 5.0~20.5% of the design deflection limitation. Furthermore, the designed roof load was only 9.9~18.9% of the ultimate equivalent distributed loads measured at truss rupture, which assures the safety of Japanese cedar roof trusses in service.

Design Procedure for Web Core Sandwich Panels for Residential Roofs

Panelized construction of residential buildings is gaining popularity due to the architectural and energy efficiency benefits that can be achieved. An important challenge to the design of panel structures for buildings is the balance between long-term structural performance and the thermal insulating requirement. In this study, foam core and web core panels are designed for residential roofs. Both panels are comprised of two face sheets and an insulating foam core. In the web core panel, thin metal webs that connect the face sheets are added to improve panel shear stiffness and enable longer spans. A design procedure is developed that considers R-value, panel deflection, core shear failure, bearing failure, and buckling of the face sheets and webs. The buckling model includes the ability of the foam core stiffness to restrain the buckling deformation. Panel designs are presented that provide R-5.3 m2K/W for roof loads of 1500, 2000, and 3000 N/m2, corresponding to climate zones in the US. It is demonstrated that the web core panel can be designed for these structural and thermal requirements with unsupported span lengths as long as 7 m, while span lengths for foam core panels are limited to 4 m. Web shear buckling and R-value are the two performance criteria that limit panel span length and depth.

Rain Loads and Flow Attenuation on Roofs

Basic relationships are derived for calculating the flow attenuation and depth of storm water on roofs. Hyetographs and corresponding hydrographs are specialized to the case of roof drainage and incorporated in methods which are presented for analysis and design of roof drains. Roof storage and outflow are characterized for various roof geometries and outflow devices. The methods are applied to examples found in the literature, including those in standards of Factory Mutual Insurance Company, ASCE, and others. Assumptions implicit in those standards are tested and their limitations demonstrated. A critical duration at which the greatest water depth and outflow occur must be found on a case-by-case basis. The critical durations can differ significantly from the fixed durations specified in standards. The corresponding maximum water depths and peak outflows can also differ accordingly. For determination of roof loads, these results will have their greatest importance in warmer climates in which the rain loads govern over snow loads. An example of design specifically for flow attenuation is also presented.

Stability Analysis of Local Thinned Shallow Spherical Roof of Oil Storage Tank

The analytical evaluation and finite element methods are used to analyze the critical stability of the shallow spherical roof of oil storage tank with an axial symmetrical corrosion region. At first, the nonlinear finite element method is adopted to calculate the global critical load of the storage tank roof, and the local corrosion region is equivalent to a circular corrosion pit with uniform depth. The results show that the tank wall and inner pressure of the stored oil have slight effects on the stability of the roof. To build the formula of local critical load of the tank roof, the circular corrosion pit is separated from the whole roof and treated as a shallow spherical shell which is elastically supported on the rest part of the roof. The equivalent support stiffness is obtained by the deformation compatibility at the edge of the corrosion pit. The resulted nonlinear stability equation is solved with a modified iteration method to determine the local critical load. The local critical load for an in-service corroded oil tank roof is analyzed by the proposed approach and the results are compared with those calculated by the conventional nonlinear finite element method with good agreement and the geometrical parameter of the corrosion region corresponding to the minimal critical load is 9.5.

Full-scale study of wind loads on roof tiles and felt underlay and comparisons with design data

Wind pressure data have been collected on the tiled roof of a full-scale test house at Silsoe in the UK. The tiled roof was of conventional UK construction with a batten-space and bitumen-felt underlay beneath the interlocking concrete tiles. Pressures were monitored on the outer surface of selected tiles, at several locations within the batten-space, and beneath the underlay. Data were collected both with and without ventilator tiles installed on the roof. Little information appears to exist on the share of wind load between tiles and underlays which creates uncertainty in the design of both components. The present study has found that for the critical design case of maximum uplifts it would be appropriate to assign 85% of the net roof load to the tiles and 15% to the underlay when an internal pressure coefficient of -0.3 is used, and to assign 60% to the tiles and 50% to the underlay when an internal pressure coefficient of +0.2 is assumed (an element of design conservatism is inherent in the apparent 110% net loading indicated by the latter pair of percentage values). These findings indicate that compared with loads implied by BS 6399-2, UK design loads for underlay are currently conservative by 25% whilst tile loads are unconservative by around 20% in ridge and general regions and by around 45% in edge regions on average over roof slopes of 15o-60o.

Seismic Design of Steel Joist Girder Structures

Current seismic design provisions emphasize detailing that results in large system ductility and energy dissipation. This may not be the best approach for flexible structures that may be able to withstand large earthquakes in the elastic range or with very limited inelasticity. Among these types of structures are tall one-story frames often constructed utilizing joist girder systems. The main objective of this study is to provide a safe and efficient seismic design methodology for steel joist girder structures; typically one-story industrial or commercial structures intended primarily to carry light roof loads. A new design procedure based on the weak column—strong beam concept is developed and experimental and analytical verification studies are described. A full-scale cyclic test and pushover analyses show that the intended mechanism can be achieved if the required design strength of the joist girder members and connection to column are based on a column flexural strength of 1.2RyMpc. This design requirement is needed in order to avoid a buckling failure of the compression angle members of a joist girder and failure of connections at the end of the joist girder.

Measurements of indoor thermal environment and energy analysis in a large space building in typical seasons

Shanghai International Gymnastics Stadium is the selected object for site-measurement. The site-measurements have been carried out during summer, winter, and the transitional seasons. Their indoor thermal environments were controlled by continuous air-conditioning, intermittent air-conditioning and natural ventilation, respectively. The site-measurement includes outdoor environment (the weather conditions and peripheral hallway), indoor air temperature distribution (the occupant zone temperature, radial temperature near upper openings and the vertical temperature distributions, etc.), and the heat balance of air-conditioning system, etc. It is found that temperature stratification in winter with air-conditioning is most obvious. The maximum difference of vertical temperature is 15 °C in winter. The second largest one is 12 °C in summer, and less than 2 °C in the transitional season. The results of measurements indicate that it is different in the characteristics on energy saving of upper openings during the different seasons. With heat balance measurements, it is discovered that the roof load and ventilated and infiltrated load account for larger percentages in terms of cooling and heating load. In this paper, many discussions on the results of site measurements show some characteristics and regulations of indoor thermal environment in large space building.

Wind effects of parapets on low buildings: Part 3. Parapet loads

As part of the study on the effects of parapets on wind-induced loads on low buildings, measurements of the pressures on parapet surfaces have been carried out. Pressures were measured on both the exterior and interior for several parapet heights, h=0.46, 0.9, 1.8, 2.7 m, and building heights, H=4.6, 9.1, 18 m, for both a uniform perimetric parapet and an isolated parapet on one wall. These data were used to quantify the local (component and cladding) and structural wind loads on the parapets. It was found that the worst structural load coefficients over all wind angles are approximately constant with h and H because of opposing trends of the pressures on the interior and exterior parapet surfaces. That is, the loads increase on the interior surface with H (as they do for roof loads), while decreasing on the exterior surface. The current structural load coefficients prescribed by the ASCE 7-02 capture this well for the building configurations considered. However, the suction component and cladding loads on the interior surface of isolated parapets are not well captured by the code.

Reliability of Light-Frame Wall Systems Subject to Combined Axial and Transverse Loads

Wood frame walls are essential subassemblies used to transmit roof, floor, wind, and seismic loads into lower stories and eventually into the foundation of light-frame structures. There has been some discussion and debate in recent years over appropriate system factors for use in the design of repetitive wall members, which typically are much smaller in the cross section than floor joists. In addition to having greater flexibility than floors, wood stud walls also may be subject to the actions of combined loads, and their load-sharing behavior may be significantly influenced by the presence of openings. As a precursor to evaluating system factors for design, this study investigated load-sharing and system effects in light-frame walls subject to combined axial and transverse loads. An analytical model was developed to account for partial composite action, load-sharing, two-way action, and openings in the wall system. The model consisted of two main components: A system model and a member model. The system ...

Commentary: Supersized vans: A supersized problem

Commentary: Supersized vans: A supersized problem