【文章內(nèi)容簡介】 Selection of Foundation Types For the base and foundation of a building, natural base should generally be adopted. If the natural base cannot meet the requirements of design or is uneconomical, artificial base may be adopted. The type selection of foundation with masonry structure shall ply with the following principles: Rigid foundation should be used as the wall column foundation. If the base is soft and uneven with a small bearing capacity and a foundation width of more than m, flexible foundation with reinforced concrete under the wall should be adopted。 When the bearing wall foundation is no more than m in depth, flexible strip foundation should be adopted. When it is ~ m in depth, flexible strip foundation or pier foundation and foundation beam may be adopted. When it is more than m in depth with solid base, pier foundation and foundation beam should be adopted。 When the nonbearing wall is no more than 240 mm in thickness and no more than m in height, the ground pad layer may be thickened without laying additional foundation. If the framed structure has no basement and the standard value of the base bearing capacity is greater than 130 kPa and even, priority should be given to single column foundation. When the standard value of the base bearing capacity is less than 130 kPa with small column space, heavy load or excessive difference between column loads which may cause great relative settlement or great change in pressibility of the main pressed layer of foundation and the adoption of single column foundation cannot meet the requirement of design, strip foundation with reinforced concrete under the column may be adopted.When part of the column foundation of a building is more than m in depth, short column foundation should be adopted. If it is no more than m in depth or individual foundation is a bit deep, the foundation pad layer may be thickened. When the load of a building with framed structure is heavy and the base is soft and uneven, crosswise reinforced concrete strip foundation may be used.When this crosswise foundation still cannot meet the requirements of design or the basement used as airraid shelter has waterproof requirement, raft reinforced concrete foundation or box foundation may be used. In the following cases, pile foundation may be used: When the base is uneven or base on bearing stratum is soft and has better lowlying stratum and the adoption of raft foundation is uneconomical。 For the important building which has special requirement for base in application and production technology or has great pressure on bottom of foundation, when the settlement estimated by natural base exceeds the allowable value。 For the highrise building, if the construction conditions do not allow to use deeplyembedded natural base or it is not evidently economical。 When the additional stress of base between units of the building interacts on each other, causing excessive uneven settlement。 When the use of pile foundation is economical because of a vast area of stacked material or thin layer of soft soil under the foundation. Calculation of Base and Foundation When the bottom area of column foundation of a factory building is determined on the basis of the base bearing capacity, the design value of pressure on the foundation base shall be taken according to the following regulations: For the column foundation of a factory building with a load of crane (not including crane for maintenance), the design value of pressure on the foundation base shall not be negative (see Fig. —1) and shall meet the requirements of the following formula: e B/6 (—1) e = M/ (N + G) (—2)where e — eccentric load (m)。 M — bending moment acting on centroid of foundation base (kNm)。 N — vertical load acting on centroid of foundation top (kN)。 G — dead weight of foundation and soil (kN)。 B — foundation width (m).When bearing load of electric bridge crane and the design value of bearing capacity of foundation f 170 kPa, the profile of pressure on the foundation base shall assume trapezoid and Pmin/Pmax . For the column foundation of a factory building with a crane for maintenance but without load of crane, when the wind load bination is taken into consideration, the design value of the pressure on foundation base is allowed to be negative (see Fig. ) and shall meet the requirements of the following formula: e B/4 (—3)When e B/6 When e = B/6Fig. —1 Pressure on column foundation base with craneWhen B/6 e B/4Fig. —2 Pressure on column foundation base without crane The bilaterally and eccentricallyloaded column foundation shall be calculated according to the following regulations: The bilaterally and eccentricallyloaded column foundation, when meeting the following formula, may be calculated according to the unilaterally and eccentrically loaded one: ey /A ≤ ex / B (—1)where A — shortedge width of foundation base (m)。 B — longedge width of foundation base (m)。 ex and ey— eccentric value of foundation base axial force at long and short sides (m). When ey ≤ A/6 and ex ≤ B/6, the pressure on foundation base shall take into consideration the influence of bending moments at the directions of X and Y. The bending moment at the cross section of column edge may be approximately calculated according to formulas (—2 and 3):where a and b—sizes of short and long edges of the column respectively。 P1 and PII— maximum pressure on the calculated foundation edges. —1 External force calculated on the foundation with bilateral eccentricity When the foundation partially leaves the soil, the design value of foundation base pressure may be calculated according