Architectural design and practice Phần 9

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Tuy nhiên, từ năm 2003 đến nay(2007) một số trào lưu kiến trúc mới theo phong cách hiện đại đã được hình thành. Tuy chưa rõ nét nhưng đã một phần thể hiện được sự hội nhập với thế giới của các kiến trúc sư Việt Nam. Bên cạnh các hình thức thường thấy ngoài đường phố, công năng sử dụng cũng được nghiên cứu nghiêm túc hơn, tạo tiện nghi cho người sử dụng tốt hơn.

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Table 12.1 Loading on wall A per metre run ©2004 Taylor & Francis
Table 12.1 (Contd) ©2004 Taylor & Francis
©2004 Taylor & Francis
Table 12.2 Loading on wall B per metre run; inner leaf ©2004 Taylor & Francis
©2004 Taylor & Francis
walls will provide the resistance to wind loading. In an actual design, the designer must of course check that the structure is safe for wind blowing east-west and vice versa. In the calculation below it has further been assumed that the walls act as independent cantilevers; and hence moments or forces are apportioned according to their stiffness. 12.5.2 Wind loads These are calculated according to CP 3, Chapter V: Part 2. We have Using ground roughness category 3, Class B, with height of the building=21.0m, from Table 3, CP3, Chapter V: Part 2 Therefore design wind speed is and dynamic wind pressure is From Clause 7.3, CP3, Chapter V: Part 2, total wind force The total maximum bending moment is total max. BM=F×h/2 where h is the height under consideration. Total BM just above floor level is given for each floor by: • 6th floor CfqAe×h/2=1.1×(1269/103)×21×3×3/2=131.9kNm • 5th floor 1.1×(1269/103)×21×6×3=527.6kNm • 4th floor (1.1×1269×21/103)×9×9/2=1187.20kNm • 3rd floor 29.313×(12×12/2)=2110.54kNm • 2nd floor 29.313×(15×15/2)=3297.70kNm ©2004 Taylor & Francis
Fig. 12.3 The variation of the factor S2 and the wind velocity along the height of the building. (Assumptions made in the design shown in full lines.) ©2004 Taylor & Francis
• 1st floor 29.313×(18×18/2)=4748.71kNm • ground floor 1.1×(1269/103)×21×21×21/2=6463.2kNm In the calculation the factor S2 has been kept constant (Fig. 12.3), which means the design will be a bit conservative. However, the reader can vary the S2 factor as given in Fig. 12.3 taken from Table 3 (CP 3) which means the wind speed will be variable depending on the height of the building. 12.5.3 Assumed section of wall resisting the wind moment The flange which acts together with the web of I-section is the lesser of • 12 times thickness of flange+thickness of web • centre line to centre line of walls • one-third of span (a) Wall A For wall A (Fig. 12.4), neglecting the outer skin of the cavity wall flange, the second moment of area is (b) Wall B The flange width which acts with channel section has been assumed as half of the I-section. For wall B (Fig. 12.5), neglecting the outer skin of the cavity wall flange, ©2004 Taylor & Francis
Table 12.3 Distribution of bending moment stresses and shear force in walls ©2004 Taylor & Francis
©2004 Taylor & Francis
©2004 Taylor & Francis
©2004 Taylor & Francis
©2004 Taylor & Francis
©2004 Taylor & Francis
12.6.2 Selection of brick and mortar combinations for wall A:BS 5628 Design vertical load resistance of wall is ( ßtf k)/ g m ( clause 32.2.1), eccentricity H ence ß =0.67 ©2004 Taylor & Francis
(Table 7 of BS 5628), m=3.5 (see section 12.3). The design loads from the previous subsection and the characteristic strengths are shown in Table 12.4 along with the suitable brick/mortar combinations. Check for shear stress: design characteristic shear fv= f mv (shear force/ area) < 0.35 +0.6gA (clause 25), f=1.4 and mv=2.5 (12.3). The value of shear force is taken from Table 12.3. For the sixth floor For the ground floor There is no need to check at any other level, since shear is not a problem for this type of structure. The BS 5628 recommends gA as the design vertical load per unit area of wall cross-section due to vertical load calculated from the appropriate loading condition specified in clause 22. The critical condition of shear will be with no imposed load just after and during the construction. 12.6.3 Load combination, wall B The design principle has been covered in great detail for wall A; hence for wall B this will be limited to the ground floor level to explain further salient points. Inner leaf wall B –ground floor level (i) Dead and imposed loads ©2004 Taylor & Francis
Table 12.4 Design load and characteristic brickwork strength ©2004 Taylor & Francis
The worst combination for this wall just above ground level also is dead+wind, and the design load is (1.96×102.5×103)/103=201kN/m. 12.6.4 Selection of brick and mortar for inner leaf of wall B The design vertical load resistance of the wall is (ßtfk)/ m (clause 32.2.1). The value of ß depends on the eccentricity of loading; hence the value of e needs to be evaluated before design can be completed. 12.6.5 Calculation of eccentricity The worst combination of loading for obtaining the value of e at top of the wall is shown in Fig. 12.6. Axial load P=(0.9×78.54+1.6×7.29) (Gk and Qk from Table 12.2) =(70.69+11.66)=82.35kN/m First floor load P1=(1.4×6.48+1.6×2.025) (see Table 12.2) =12.31kN/m ©2004 Taylor & Francis
BM at centre of the panel=627.8×(Cpe+CPi)h2×0.104×1.4 =627.8×(1.1+0.2)×(2.85)2×0.104×1.4 =964.6Nm/m (Cpe and Cpi from CP3, Chapter V: Part 2) (BM coefficient for four-sided simply supported panel is 0.104; table 3.1, BS 8110) (since both leaves are of same stiffness) where Resultant (b) Wind blowing west-east direction The panel B is not only subjected to dead and imposed loads, but also subjected to wind loading from west to east direction. Then (the bending moment induced due to wind loading acts against those due to the vertical load). Since resultant eccentricity of case (b) is greater than case (a), case (b) eccentricity is considered in the design. ©2004 Taylor & Francis
12.6.6 Calculation of characteristic compressive stress fk for wall B (inner leaf) 12.6.7 Design of the outer leaf of the cavity wall B in GF Load combination: • Windward side ©2004 Taylor & Francis