混凝土结构原理.ppt

,混凝土结构原理 (1-2章),CHAPTER 1 INTRODUCTION(绪论),1. Problems for ponderation(思考题) 1.1 Explain the effect of that the concrete beam has steel reinforcing bars embedded at the bottom under loading. （解释在底部配有钢筋的混凝土梁在荷载作用下的影响） A plain concrete beam under loading will be cracked at the tension region of the mid-span(跨中) and the beam will fail suddenly when the load reach its limit value. But reinforcing bars embedded at the bottom of the concrete beam can take up the tension there after the concrete is cracked .when the steel approaches yielding stress ,the crack are so large offering the warning (预警)that the beam is going to fail. 提高梁的承载能力和变形能力,1.2 Why can work together the concrete and reinforcement? (钢筋和混凝土为什么可以共同工作） Concrete and reinforce can work together because : 1)There is a sufficiently strong bond between the two materials . 2)The thermal expansion coefficients(线膨胀系数) of the two materials are similar. 3)The concrete coverer can protect the steel bars from rusting(腐蚀).,1.3 Explain the advantages and the disadvantages of reinforced concrete structure. （解释钢筋混凝土结构的优点和缺点） Advantages: 1)durability(耐久性) 2）fire resistance(耐火性) 3）high stiffness(刚度高) 4) locally available resources;(易于就地取材) 5)cost effective; 6) entirety(整体性好); Disadvantages: 1)large dead mass(自重大) 2)long cure period (养护周期长） 3)easily cracked; (容易开裂),CHAPTER 2 MECHANICAL PROPERTIES OF REINFORCED CONCRETE MATERIALS (钢筋混凝土材料的力学性能),1. Problems for ponderation(思考题) 2.1 Explain the difference of stress-strain relationship between the mild steel bars and the hardening steel bars. (分析有明显屈服点钢筋和没有明显屈服点钢筋的应力应变关系有何不同),应力应变曲线,d(其对应极限抗拉强度),2.2 Why the strength of the steel beyond the yielding strength can not be utilized and the yielding stress is all the strength available for structural design? （在结构设计中，为何将屈服强度做为钢筋的强度取值而不能利用超过屈服强度以后的强度） When the strength of steel beyond the yielding strength , the steel enter into the stage of flow(塑性流动阶段) ,and the deformation(变形) will become larger than before distinctly. The steel may enter the hardening stage(强化阶段), the large deformation during the flow make the structure cant be serviceable.(适用性),2.3 What is the cubic compressive strength? Explain the factors that affect the . （什么是混凝土立方体抗压强度，影响其强度的主要因素） The cubic compressive strength is the compressive stress of a cubic specimen(试样) with side length of 150mm ,cured for 28 days under standard test method (temperature is at 203, humidity 90%),test by the standard test method (surface of specimen is not lubricate(润滑) with grease(油脂) , loading speed increase in 0.150.25MPa/s ). The factors affect the strength of concrete : 1). The size and shape of the specimen ;2) Age and curing conditions; 3). The speed of Stressing; 4).The orientation of stress relative to direction of casting(荷载方向和浇筑方向的关系).( 5) .The condition of lateral constraint.(侧向约束)。,2.4 What are the characteristics of the constitutive relation of concrete in compression? (混凝土受压状态下本构关系的特点),反弯点,收敛点,残余应力,2.5 How can we define the grade of concrete? （如何确定混凝土强度等级） We use the compressive strength to define the grade of the concrete. The cube strength of concrete is classified into following 14 grades: C15, C20,C70,C75,C80. The “C” stands for “concrete”, and the following numerals indicate the standard cube strength of the concrete in MPa. .,2.6 List the characteristics of concrete strength under bi-axial（双轴） or tri-axial（三轴） loads. （解释在双轴受力和三轴荷载的情况下混凝土强度的特点） 2.7 Explain the terms of initial modulus of elasticity , tangent modulus of elasticity , the secant modulus of elasticity and the coefficient of elasticity. （解释初始弹性模量，切线弹模，割线弹模(变形模量)和弹性系数） The initial slope(初始角度) of the tangent to the curve is defined as “initial modulus of elasticity”. the slope of the tangent to a point of the curve is defined as “the tangent modulus of elasticity”. And the slope of the straight line that concretes the origin to a point of the curve is defined as “the secant modulus of elasticity”。In elasticity analysis the coefficient of elasticity can be taken as “ ”,2.8 Define the terms of creep and shrinkage of concrete .List the main factors which influence creep and shrinkage. （什么是混凝土的徐变和收缩，影响它们的主要因素是什么） Creep :or plastic flow, is the increase in strain with time due to sustained load(长期荷载). Shrinkage : the volume of the concrete shrink when the concrete harden(硬化) in the air. The factors which influence creep and shrinkage are: 1) amount of cement (水泥用量);2)aggregate;(骨料) 3)water-cement ratio;(水灰比) 4)size of element;(构件体积) 5) medium ambient condition; (环境)6)amount of reinforcement;(钢筋量) 7) admixture;(外加剂)8) type of cement.(水泥种类),2.9 List the factors affected the bond strength between the concrete and steel. （列出影响钢筋和混凝土之间的粘结的因素） 1)adhesion (粘结力)between the concrete and reinforcing element.2)gripping effect resulting from the drying shrinkage of the surrouding concrete and the shear interlock between the bar deformations and the surroundingconcrete.3)frictional(摩擦力) resistance to sliding and interlocks that the reinforcing element is subjected to tensile stress. 4)effect of concrete quality and strength in tension and compression. 5)mechanical anchorage effect(锚固作用) of the ends of bars through development length, splicing, hooks, and crossbars.6) Diameter, shape, bond length, and spacing of reinforcement as they affect crack development. 7) The percentage ratio and yielding strength of the stirrups.(箍筋) 8)The height of the covered concrete near embedded reinforcement of concrete members .(保护层厚度),2.10 Define the term of the development length of reinforcement. （钢筋锚固长度的定义） The embedded length of the reinforcement must be sufficient to the development by the bond of maximum tensile force in the reinforcement .The length required to develop the yield strength(屈服强度) of the reinforcement is called the development or anchorage(锚固) length.,2. Problems for solution (计算题) 2.1. A stress-strain relationship is shown as the following , the stress-strain curve of ascending segment is , and that of descending segment is , the axially-compressive strength of concrete is , find the value of initial modulus of elasticity . if the stress of concrete at point C is , find the values of tangent(切线) modulus of elasticity ,the secant modulus of elasticity and the coefficient of elasticity v at point C.,C,= 2*20/0.002 = 2*104 MPa =0.9*104 MPa =0.8*20/0.0011=1.45*104MPa =1.45/2=0.725,2.2 Determine the values of development length by the specification in Chinese Code.,