Some studies on the ultimate load capacity of arches and arch dams

Abstract

The behaviour of a plain concrete rectangular section under an eccentric thrust, up to failure, may be studied using an appropriate strain pattern and a suitable stress-strain curve for concrete. The curve obtained using Whitney抯 stress block is conservative and easy to adopt. i) The arches considered for experimentation failed in four different types, and each type has its own characteristic feature. ii) Arches failing in Type 2 developed 揾inges,� allowing for rotation as seen in reinforced concrete beams. iii) The theoretical methods developed in Chapter 2 do not show full agreement with all the arches individually. No single theory may be effectively used to predict the ultimate load capacity fully for all the arches. However, the method using Equation 2.10 showed better agreement compared to all the other theories. iv) Thin cylinder theory (2.7.b) and Equation 2.10 may be suitably used to predict the ultimate load capacity of arches in the two zones described.

In the linear programming method of analysing arch dams, the following conclusions may be drawn: i) Since the number of divisions into which the height of an arch dam is divided does not appreciably alter the load capacity, for an approximate study the height of a dam may be divided into 6 to 8 elements. ii) Of the various theories used for estimating arch capacity, the thrust criterion gives the maximum value and the stress factor gives the least value. iii) Since the arch dam will have the maximum carrying capacity under a triangular load, its ultimate load capacity will be rapidly reduced under overloads due to overtopping. iv) Variations in the shape of the valley and the thickness of the dam can be easily taken into account in this method of estimating the ultimate load capacity of an arch dam. v) It is not possible to trace the progressive failure modes of a dam when estimating the ultimate load capacity of an arch dam using the linear programming method. vi) For dams in rectangular valleys, three different zones are observed in the slenderness-valley ratio diagram. These three zones are based on the three different types of failure of the components of the dam, viz., arches and cantilevers.