Resource Allocation Auctions Within Firms

There is growing interest in the use of markets within firms. Proponents have noted that markets are a simple and efficient mechanism for allocating resources in economies in which information is dispersed. In contrast to the use of markets in the broader economy, the efficiency of an internal market is determined in large part by the endogenous contractual incentives provided to the participating, privately informed agents. In this paper, we study the optimal design of managerial incentives when resources are allocated by an internal auction market, as well as the efficiency of the resulting resource allocations. We show that the internal auction market can achieve first-best resource allocations and decisions, but only at an excessive cost in compensation payments. We then identify conditions under which the internal auction market and associated optimal incentive contracts achieve the benchmark second-best outcome as determined using a direct revelation mechanism. The advantage of the auction is that it is easier to implement than the direct revelation mechanism. When the internal auction mechanism is unable to achieve second-best, we characterize the factors that determine the magnitude of the shortfall. Overall, our results speak to the robust performance of relatively simple market mechanisms and associated incentive systems in resolving resource allocation problems within firms

An experimental and numerical investigation of concrete dam joints

This communication summarises the results of a comprehensive investigation aimed at improving the understanding of the cyclic behaviour of concrete dam joints, covering both experimental and numerical aspects. In the laboratory work, a jointed concrete block is subjected to reversed cyclic slip at imposed normal stress. The specimen is intended to represent a portion of either a lift joint or the dam-foundation interface. Aspects of novelty can be found in the test setup and in the specimen size (90×70×30 cm). The tests performed so far, though limited in number, have allowed to assess and approximately quantify for concrete the characteristic influence of joint roughness on the observed shear strength and dilatancy. A generalised interface model is proposed in order to describe the joint behaviour, including all the phenomena commonly accounted for in mixed mode fracture of cohesive quasi-brittle materials and the effects of surface roughness. This result has been obtained by combining a fracture-mechanics based interface model for concrete with a cyclic one for rock joints. Simulations carried out so far evidence a good qualitative agreement with results available in literatur

The influence of moisture on the fracture behaviour of concrete loaded in dynamic tension

Dynamic tests demonstrate an extensive rate effect on the tensile strength as well as the post-peak behaviour beyond loading rates of about 50 GPa/s. One of the possible explanations for the observed rate effects on the fracture behaviour is enhanced resistance by moisture in the pores. To study the influence of the moisture content and pore structure on the rate dependency, different moisture contents and concrete types are used and tested at three loading rates. From the test results it is concluded that the moisture volume, porosity and pore structure play an important role for tensile strength as well as the fracture process. The NMR tests showed that the water in the capillary pores causes the strength increase and not the water in the gel-pores. From the analysis of the experimental results it is concluded that for loading rates < 50 GPa/s, the main cause for the observed strength increase is the viscous behaviour of concrete. For loading rates beyond 50 GPa/s, also rate effects due to limitations on crack propagation contribute to the observed strength increase for all moisture contents and concrete types. Concerning the post peak response for rates > 50 GPa/s, the additional resistance is due to additional micro cracking, the moisture in the capillary pores and the limited crack propagation velocity

Algorithm for Non-proportional Loading in Sequentially Linear Analysis

Sequentially linear analysis (SLA) is an alternative to the Newton-Raphson method for analyzing the nonlinear behavior of reinforced concrete and masonry structures. In this paper SLA is extended to load cases that are applied one after the other, for example first dead load and then wind load. It is shown that every nonlinear analysis step can be made in just two linear elastic analysis steps. The proposed algorithm is extremely robust, which is demonstrated in a prestressed concrete beam analysis. A comparison is made between results of SLA and Newton-Raphson with arch length control

9th International Conference on Fracture Mechanics of Concrete and Concrete Structures DEBILITIES AND STRENGTHS OF FEM-BASED CONSTITUTIVE MODELS FOR THE MATERIAL NONLINEAR ANALYSIS OF STEEL FIBER REINFORCED CONCRETE STRUCTURES

Abstract: During the last decades several improvements have been made on the numerical simulation of concrete type structures by modeling the relevant nonlinearities presented by concrete and reinforcements, as well as their interactions. With the advent of new cement based materials, such is the case of fiber reinforced concrete (FRC), new challenges and difficulties are placed to the computational mechanics community. This work discusses debilities and strengths of constitutive models implemented under the framework of the finite element method (FEM) for the simulation of FRC structures, and points out areas deserving further specific research for more reliable modelling strategies

Simulation of dynamic behavior of quasi-brittle materials with new rate dependent damage model

Stress-based nonlocal model, Damage, Rate dependency, Dynamic crack-branching Abstract. In concrete often complex fracture and fragmentation patterns develop when subjected to high straining loads. The proper simulation of the dynamic cracking process in concrete is crucial for good predictions of the residual bearing capacity of structures in the risk of being exposed to extraordinary events like explosions, high velocity impacts or earthquakes. As it is well known, concrete is a highly rate dependent material. Experimental and numerical studies indicate that the evolution of damage is governed by complex phenomena taking place simultaneously at different material scales, i.e. micro, meso and macro-scales. Therefore, the constitutive law, and its rate dependency, must be adjusted to the level of representation. For a proper phenomenological (macroscopic) representation of the reality, the constitutive law has to explicitly describe all phenomena taking place at the lower material scales. Macro-scale inertia effects are implicitly simulated by the equation of motion. In the current paper, dynamic crack propagation and branching is studied with a new rate-dependent stress-based nonlocal damage model. The definition of rate in the constitutive law is changed to account for the inherent meso-scale structural inertia effects. This is accomplished by a new concept of effective rate which governs the dynamic delayed response of the material to variations of the deformation (strain) rate, usually described as micro-inertia effects. The proposed model realistically simulates dynamic crack propagation and crack branching phenomena in concrete