Calculation Model For Tensile Membrane Effects Of Reinforced Concrete Slabs At Ambient And Elevated Temperature

In general, reinforced concrete (RC) slabs undergo large deflections when they aresubjected to extreme loads, e.g. fire, blast and impact. Due to tensile membrane action,RC slabs can still keep steady even under quite large deflections. Therefore, tensilemembrane action plays an important role in maintaining the integrity of structures. Inaddition, it provides highly probability that the persons and important properties in theattacked buildings can be rescued and saved with adequate time.Membrane action involves compressive membrane action corresponding to lowdeflections, and tensile membrane action to larger deflections. During the past years,compressive membrane action was widely studied, while less attention was paid ontensile membrane action. Based on the above consideration, tensile membrane action ofRC slabs subjected to large deflections is taken as the research objective of this thesis.Considering the influence of tensile membrane action, the load-carrying capacity of RCslabs, at ambient and elevated temperature, is studied from both theoretical andexperimental aspects. The main contents are summarized as follows:1) The influence of tensile membrane action on the load-carrying capacity of RCslabs is not incorporated in the conventional yield line theory. In this thesis, the tensilemembrane action is assumed to be provided by the vertical component of the steelforces at the section of yield lines or the plastic energy dissipation due to the extensionof reinforcements along yield lines after the formation of mechanism of plastic hingeline. Then, a new model is proposed to estimate the load-carrying capacity consideringthe influence of tensile membrane action. The new model is validated and comparedwith other similar models proposed by others using the small-scale experimental resultshome and abroad. It is illustrated that the new model has adequate accuracy to estimatethe load-carrying capacity of RC slabs subjected to large deflections.2) In order to examine the performance of the new model, a serial full-scaleconcrete slabs tests were carried out at ambient temperature. All the slabs were tested tolarge deflections, and six one-way concrete slabs, two rectangular and two square slabswere contained. The one-way concrete slabs had three different edge conditions, i.e. twoedges simply supported, two edges clamped, one edge simply supported and one edgeclamped. The edges of all the two-way concrete slabs were all simply supported. According to the after-test observations, the assumptions used in the model arereasonable. That is to say that tensile membrane action is do provided by the verticalcomponent of the steel forces at the section of yield lines or the plastic energydissipation due to the extension of reinforcements along yield lines. Through studyingthe test data, the proposed model is proved to be effect. Additionally, the formula usedin the proposed model, to calculate the deflections for the characteristic points, ismodified. Using the proposed model, main factors having influences on the tensilemembrane action are examined.3) Several fire tests of full-scale concrete slabs are summarized, including two-wayslabs with four edges simply supported and four edges clamped respectively, one-wayslabs with two opposite edges simply supported, and multi-bay continuous concreteslabs. Through interpreting the test observations, failure modes of the test slabs aresummarized. Besides, tensile membrane action of RC slabs is proved to occur in fire,and its mechanism is explained. Incorporating the high-temperature effects, a newcalculation model is further presented to calculate the load-carrying capacity of concreteslabs in fire. Through studying the fire test results, the new presented model is proved toexactly predict the load-carrying capacity of RC slabs.