Unit 3 Stress and Deformation应力与变形.ppt

Unit Three Stress and Deformation 应力与变形 Leading in Dialogue Text Exercises Guided Writing Teaching Steps Leading in Force Deformation Stress is the physical pressure or other forces exerted on an object. Deformation in any direction is the total change in the dimension of a member in that direction. Work platform Anchor bolts rebar formwork concrete pre-stressing operating fixing formwork A: Since many pre-stressing reinforced concrete components are adopted in this project , it is necessary to have a look at the pre-stressing operating . exerting tension Dialogue B: The rebar is pre-stressed first by a certain tension force and fixed on both ends. Then we fix the formwork and non-prestressed rebar, and then pour concrete. After the concrete reaches the designed strength , the pre-stressed rebar are released . pouring concrete releasing rebar offset the tension force A: The strength from the pre- stressing members is transferred to the concrete , isn’t it ? B: Yes. The pre-stressed concrete will offset some or all the tension force when it is under the situation of tension strength. rebar Pressure A: Are there any differences between the pre-stressed concrete and non-prestressed concrete in concrete pouring? B: In order to reduce the concrete shrinkage under the pre-stressing , the pre-stressed concrete should be poured continuously in one time without construction joints . the ratio of water and cement should be low and the aggregate should be selected in better quality . construction joints A: When can the fixtures of the pre–stressed rebar be removed ? B: It depends on whether the concrete strength reaches the designed value or not. At least the test should show that the result is up to the standard. if the fixture are released too early , it will cause lots of strength loss and even serious quality problem . be up to the standard: reach the standard 达到标准 e.g. your recent work just hasn’t been up to standard at least: n