Wind Moment design analysis - Statistics Project Example

Wind moment design analysis Presented to [Teacher’s In Partial Fulfillment of the Requirements of [Project d Contents Wind moment design analysis 3 1.0. Introduction 3 1.1.Benefits of wind moment design 5 1.2.Connections 5 1.3.Frame properties 7 1.4.Individual components 9 1.5.Loading 9 1.6.Design of major axis frames 10 2.0. Project analysis 10 2.1. Analysis at the ultimate limit state 10 2.2. Framing and loading 11 2.3. Loading 11 2.4. Design 13 2.5. Wind analysis 13 2.6. Notional horizontal forces and analysis 14 2.7. Ultimate limit state 15 2.7.1. Dead load plus imposed loading 15 3.CONLUSION 16 REFERENCES 16 Appendix 19 A: Contents of capacity tables 19 Appendix c: Values of ψ factors for buildings 20 Wind moment design analysis 1.0. Introduction According to the euro code 0 ‘basis of structural is, ‘a structure is an organized combinations of connected parts designed to carry loads and provide adequate rigidity.’ Unbraced steel rely on the stiffness and the resistance of its frame to wind forces. In the initial development plans .the moments induced by wind were assumed to be relatively negligible as compared to plastic moment’s capacity of the construction beams. In other words the forces of the wind were based on an assumption of uniform pressure of 20 pfs (956 pa) on the projected building. To counteract this old technological view, wind moments or wind connections remain as the only simple method design for multipurpose frames. Though developed earlier, the design was initially developed to compensate for the wind loads while the preferred connection method was by angles, bolting or/and small T-stab sections this were used to carry the column flanges and the bam flanges. Wind moment apply to row rise frames of to four or less. The method assume that when structure are subject to wind loads. The connections behave normally as rigid joints (figure1) and that under vertical loads, the connections act normally simple connections; figure 2. Figure1: Internal moments and forces according to the wind-moment method Figure 2: Frame assumptions for the wind-moment method In the design of the wind moments, the frames are braced to prevent minor axis sway of columns at each floor level and roof level. It should also ensure that the frames also do not sway in either principle directions. 1.1. Benefits of wind moment design Designer view this deign as having more advantage as compared to the conventional design grades. They are simple and suitable for manual calculations. The frames of the structure are taken to be statically determinate. Internal forces and moments are not depended on the relative stiffness of the individual structural members. In constructions, this methodological design is relatively simple of the steelwork in comparison to full rigid construction. It has been determined that the steelwork contractors are always concerned with making steel work connections in the workshops. This increases the cost of construction by as high as 50% of the total cost of the completely erected work. With the wind moment design, the connections are simplified and thus reduced fabrication input. This has a notable reduction in the total cost of steel frame erection. 1.2. Connections Since the frame is subject to lateral wind, it is essential for the wind moment design to embracethe connection that should be ductle enough to accommodate rotations. Moment connection as shown in figure 3 offers the required support to provide the same moment resistance to both sagging and logging. Among the significant properties, of this kind of connections is that they should be rigid, have partial strength and the connection should be ductile, figure 4 below provide the full explanation with the key points of the design. Figure3; Typical wind-moment connection A the same time all the connections should strictly adhere to the set out standards. The choice of the end plates, thickness and bold spacing should be located in relation to the strength and the size of the bolts and of the welds as indicated in appendix A. Figure 4; Moment-rotation characteristics of typical wind-moment connections 1.3. Frame properties Wind moment method should only apply on frame that comply with the following requirements The geometry of the frame should be within the ranges shown in Table 1. The width of each bay should be constant over the height of the frame. The structure should be capable of being represented by a series of unbraced plane frames, each comprising a regular arrangement of orthogonal beams and Columns. Beam layouts should comply with one of the options shown in Figures 5, 6 and 7 Table 1; Proportions of frames suitable for use of the wind-moment method Figure5: Beam layout with floor spanning to major axis beams Figure6: Beam layout with floor spanning to secondary and minor axis beams Figure7; Beam layout with floor spanning to intermediate and major axis beams 1.4. Individual components This refers to the member of the frame. Each individual components need to be within this conditions; The steel grade can be S355 or S275 but it should be emphasized that the same design grade must use the same members of the frame. Horizontal members should be hot rolled universal columns. Members should be composite Vertical members should be hot rolled universal sections. As described in appendix A, connections should be flush end plates To resist moments , the column should be rigidly connected 1.5. Loading Wind loads can either be derived using either BS6399-2 or CP3 chapter V, part 2. It should be based on the frame limits in table 2 below. Table2: Frame loading limits 1.6. Design of major axis frames Major axis for simplicity axis frames is applied to the frame that is effectively braced at the roof and each floor level to prevent sway about the minor axes. Sway can be prevented by cross bracing or attaching other systems to the right core as shown in fig 8. Figure8: Plane frames braced against out-of-plane sway 2.0. Project analysis 2.1. Analysis at the ultimate limit state From our explanations above on the design structure specifications, figure 9 below represents a frame which is braced out of plane in order to prevent sway that occur about the minor axis of the columns the flame has been constructed to conform with a frame layout which is effectively braced out against sway and floor layout consisting of primary beams only with roofing and floor spanning as shown in figure 5. 2.2. Framing and loading The dimensions of the flame conform to the applications range that is specified in section 1.5. This is clearly shown in figure 9: In the bottom storey; bay width: storey height = = 1.2 In the above bottom storey, the bay width: storey height = =1.5 Greatest bay width to the smallest bay width== 1 Storey height bottom storey= 5m< 6m Storey height (other storey) = 4m< 5m 2.3. Loading This conforms to the range applications which is described in section 1.5; These loads used in design include: Roof Floor Dead load 2.6 kN/m 2 6.5 kN/m 2 Imposed load 0.60 kN/m 2 2.25 kN/m 2 Table 3: dead and imposed loads on the roof and the floor of the structure The structure will be designed though with same member in the frame to accommodate for the size of the frames and the sized. Base on the appendix C, load combination at the roof can be calculated to accommodate all the dimensions of the storey building. Figure 9: Frame arrangement and applied wind loads for typical internal frame On the frame structure the following are eminent: Frames located at 6.0m centers longitudinally Roof Dead load 2.6 kN/m 2 Imposed load 0.60 kN/m 2 Floors Dead load 6.5 kN/m 2 Imposed load 2.25 kN/m 2 In the figure9; wind forces are equated to a basic wind speed that is not less than 37m/s (CP3: chapter V: part 2). 2.4. Design The members of the wind moment design were selected and adjoined using the rules given in BS5950-1990. More properties like the member capacities were obtained from the capacity tables in BS5950: part 1:1990. 2.5. Wind analysis Figure 10 below represents the wind loads on the design structure. Figure 10: Frame analysis under wind loads (columns) From the structural design, there are 4 storeys’ that can be outlined. They encounter different shear and bending forces as shown: 2.6. Notional horizontal forces and analysis Notional horizontal force = 0.005 (1.4 Dead + 1.6 Imposed) Roof H = 0.005 (1.4 × 2.6 + 1.6 × 0.6) × 24 = 5.76 kN Floor H = 0.005 (1.4 × 6.5 + 1.6 × 2.25) × 24 = 10.3 kN From the calculations above, the axial forces generated in the beams and columns by the notional horizontal forces are small and may be neglected. Figure 11: roof beam 2.7. Ultimate limit state 2.7.1. Dead load plus imposed loading Design load for ULS: W = (1.4 × 2.6 + 1.6 × 0.6) × 6 = 20.97 kN Sheet 1 Taking advantage of the 10% restraint moment at the end of the beams The maximum moment at the centre of the span M =×= 1.59 Section is Class 1 plastic. The beam is fully restrained. Moment capacity (Mcx ) In order to provide directional restraint to the columns, the moment capacity is limited to 0.9 Mcx. Section 0.9 Mcx = 0.9 × 233 = 210 kNm > 194 kNm 3.CONLUSION From the results and discussions several conclusions can be deduced; 1. Wind moment designs method can be used to design unbraced storey building of up to 4 storey’s 2. To reduce the possibility of sway deflection, the design of the building should be controlled by the serviceability limit state. 3. All the flames that are used to designing the structure need stiffer columns to be able to resist any horizontal sway deflections. REFERENCES ANDERSON, D. and KAVIANPOUR, K. Analysis of steel frames with semi-rigid connections Structural Engineering Review, Vol. 3, 1991.BCSA/SCI, 1995 2. BRITISH STANDARDS INSTITUTION BS 5950: Structural use of steelwork in building BRITISH STANDARDS INSTITUTION BS 6399: Loading for buildings Part 1: 1984: Code of practice for dead and imposed loads Part 2: 1995: Code of practice for wind loads Part 3: 1988: Code of practice for imposed roof loads BSI. BROWN, N.D., ANDERSON, D. and HUGHES, A.F. Wind-moment steel frames with standard ductile connections Civil Engineering Research Report CE61, University of Warwick, 1999 (Submitted as a paper to the Journal of Constructional Steel Research) COUCHMAN, G.H. Design of semi-continuous braced frames (SCI P183) The Steel Construction Institute, 1997 P263: Wind-moment Design of Low Rise Frames This material is copyright - all rights reserved. Reproduced for IHS Technical Indexes Ltd under license from The Steel Construction Institute on 15/8/2005 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Licensed copy: unawares, , 28/04/2014, Uncontrolled Copy, © Steel Construction Institute SCI-P263 Wind-moment Design of Low Rise. GIRARDIER, E.V. The role of standardized connections New Steel Construction, Vol. 1, No. 2, February 1993, pp. 16-18 3. HENSMAN, J. and WAY, A. (SCI P264) Wind-moment design of unbraced composite frames The Steel Construction Institute, 2000 BRITISH STANDARDS INSTITUTION CP3: Basic data for the design of buildings Chapter V: Loading Part 2: 1972: Wind loads BSI, 1972. Part 1:1990: Code of practice for design in simple and continuous construction: hot rolled actions BSI, 1990 Steelwork design guide to BS 5950: Part 1: 1990 Volume1: Section properties and member Capacities (5th Edition) (SCI P202) The Steel Construction Institute, 1997. TAHIR, M.Md. and ANDERSON, D. Wind-moment design of unbraced minor axis steel Frames Civil Engineering Research Report CE63, University of Warwick, 1999 (Submitted as a paper to the Structural Engineer). THE BRITISH CONSTRUCTIONAL STEELWORK ASSOCIATION/THE STEEL CONSTRUCTION INSTITUTE Joints in steel construction: Moment connections (SCI P207) THE BRITISH CONSTRUCTIONAL STEELWORK ASSOCIATION/THE STEEL CONSTRUCTION INSTITUTE Joints in simple construction Volume 1: Design Methods (2nd Edition), 1993 (SCI P205) Volume 2: Practical Applications, 1992 (SCI P206) WOOD, R.H. and ROBERTS, E.H. A graphical method of predicting sideway in the design of multi-storey buildings Proceedings of the Institution of Civil Engineers Part 2, Vol 59, pp. 353-372, June 1975.. ANDERSON, D. Design of multi-storey steel frames to sway deflection limitations Steel framed structures: Stability and strength (ed. R. Narayanan), pp. 55-80 Elsevier, 1985. Appendix A: Contents of capacity tables Appendix c: Values of ψ factors for buildings Read More