technological difficuties will a designer of tall building meets.doc

C5 It is this devintion in the composition of a reinforced concerte section from the bornogeneity of standard wood or steel sections that requires a modified approach to the basic principles of sctuctural design. The two components of the beterogeneous reinforced concrete section are to be so arranged and proportioned that optmal use is made of the materials involved. This is possible because concrete can easily be given any desired shape by placing and compacting the wet mixture of the constituent ingredients into suitable forms in which the plastic mass hardens. If the various ingredients are properly proportioned, the finished product becomes strong, durable,and ,in combination with the reinforcing bars, adaptable for use as main members of any structural system. 由于钢筋混凝土截面在均质性上与标准的木材或钢的截面存在着差异，因此，需要对结构设计的基本原理进行修改。将钢筋混凝土这种非均质截面的两种组成部分按一定比例适当布置，可以最好地利用这两种材料。这一要求是可以达到的，因混凝土由配料搅拌成湿拌混合物，经过振捣并凝固硬化，可以做成任何一种需要的形状。如果拌制混凝土的各种材料配合比恰当，则混凝土制成品的强度较高，经久耐用，配置钢筋后，可以作为任何结构体系的主要构件。 The techniques necessary for placing concrete depend on the type of member to be cast: that is ,whether it is a column, a beam, a wall, a slab, a foundation, a mass concrete dam, or an extension of previously placed and hardened concrete. For beams, columns, and walls ,the forms should be well oiled after cleaning, and the reinforcement should be cleard of rust and other harmful materials. In foundations, the earth should be compacted and thoroughly moistened to about 6 in , in depth to avoid absorption of the moisture present in the wet concrete. Concrete should always be placed in horizontal layers which are compacted by means of high-frequency power-driven vibrators of either the immersion or external type, as the case requires, unless it is placed by pumping. It must be kept in mind, however ,that overvibration can be harmful since it could cause segregation of the aggregate and bleeding of the concrete. 浇筑混凝土所需的技术取决于即将浇筑的构件类型，例如：柱、梁、墙、板、基础，大体积混凝土水坝或者继续延长已浇筑完毕并且已经凝固的混凝土等。对于梁柱强等构件，当模板清理干净后应该在上面涂油，钢筋表面