Deflection control of prestressed concrete elements considering uncertainties

Excessive deflections can affect serviceability e.g. by causing damage to connecting building components and resulting in problems related to drainage in roof slabs. The deflections of a reinforced or prestressed concrete structure are subject to change over time, among others due to creep and shrinkage of concrete and relaxation of the steel used for prestressing. This structural response can be predicted as a function of time using calculation models available in literature which incorporate methods to account for these time-dependent effects. The deflection of prestressed elements is the result of the application of external loads and the prestressing of the tendons, which are two opposing actions (with respect to deflections). The resulting total deflection of the concrete element is very sensitive to small changes to the input variables used during design. A design method for deflection control is proposed which limits the deflection during the lifespan of the elements by defining requirements for the prestressing arrangement accounting for parameter uncertainty. An example of a prestressed beam is given in which the deflection is optimized over its lifetime

SHM strategy optimization and structural maintenance planning based on Bayesian joint modelling

In this contribution, an example is used to illustrate the application of Bayesian joint modelling in optimizing the SHM strategy and structural maintenance planning. The model parameters were evaluated first, using the Markov Chain Monte Carlo (MCMC) method. Then different parameters including expected SHM accuracy and risk acceptance criteria were investigated in order to give an insight on how the maintenance planning and life-cycle benefit are influenced. The optimal SHM strategy was then identified as the one that maximizes the benefit

A parametric study on buckling of R/C columns exposed to fire

Buckling of concrete columns is a major issue in fire design, since heating of the columns will result in loss of stiffness and strength in the outer concrete layers. In the Dutch concrete code NEN 6720 (NEN, 1995), a quasi-linear theory of elasticity (KLE) method is provided for columns at ambient temperature. However, no literature is available showing whether this method could be adopted for elevated temperatures. Hence, an efficient calculation tool is needed to validate the applicability of this method in case of fire. As a first step, a cross-sectional calculation tool is introduced to calculate interaction curves of columns at ambient temperature. Further, the interaction diagrams obtained with this numerical method as well as the stiffness method provided in (Eurocode, 2004) and the KLE method are compared. Then, an assumed formula in the KLE-method for the nominal stiffness calculation is discussed considering interaction curves of columns in case of an ISO 834 fire. Finally, parameters like the fire duration and the slenderness ratio are investigated

Classes of decision analysis

The ultimate task of an engineer consists of developing a consistent decision procedure for the planning, design, construction and use and management of a project. Moreover, the utility over the entire lifetime of the project should be maximized, considering requirements with respect to safety of individuals and the environment as specified in regulations. Due to the fact that the information with respect to design parameters is usually incomplete or uncertain, decisions are made under uncertainty. In order to cope with this, Bayesian statistical decision theory can be used to incorporate objective as well as subjective information (e.g. engineering judgement). In this factsheet, the decision tree is presented and answers are given for questions on how new data can be combined with prior probabilities that have been assigned, and whether it is beneficial or not to collect more information before the final decision is made. Decision making based on prior analysis and posterior analysis is briefly explained. Pre-posterior analysis is considered in more detail and the Value of Information (VoI) is defined

Derivation of practical reliability-based post-fire assessment tools for structural elements

A practical reliability-based post-fire assessment method has been presented in earlier work which evaluates the maximum allowable characteristic value of the imposed load effect on concrete elements after being subjected to fire. The method is known as the ReAssess method and can be extended to cover the post-fire assessment of other material types, structural members and limit states. This extension however requires knowledge of the methodology underlying the derivation of the basic equations. In this paper a detailed overview of this methodology is presented for the first time, incorporating all the steps from the definition of the limit state problem up to the verification of the reliability obtained when applying the method. The presented methodology allows for the development of practical reliability-based post-fire assessment tools to a broad range of structural members. An example derivation is given illustrating the application of the presented concepts to the post-fire bending limit state for a simply supported concrete slab

Parametric study of the load-bearing mechanisms in RC beam-grids to resist progressive collapse

Recently, several structural failures demonstrated the disastrous consequences of progressive collapse and raised the awareness of the engineering community. However the low probability of progressive collapse makes it uneconomical to design every building against progressive collapse using conventional design methods. Furthermore in most cases the initiating events of progressive collapses are unknown during the design. As such, consideration of secondary load-carrying mechanisms can be an effective alternative. These mechanisms include compressive arch action (CAA) and tensile catenary action (TCA) in reinforced concrete (RC) beams. Several researchers have investigated the effects of CAA and TCA experimentally and numerically in individual RC beams. However to date limited studies have been carried out to study these mechanisms in RC beam-grids. Hence in this contribution a validated numerical model is developed to study and quantify the individual contributions and development of the different mechanisms in RC beam-grids. Parametric studies are performed in relation to the influence of the aspect ratio of the grid, reinforcement ratio and ultimate reinforcement strain

Strain and crack development in continuous reinforced concrete slabs subjected to catenary action

Several structural calamities in the second half of the 20th century have shown that adequate collapse-resistance cannot be achieved by designing the individual elements of a structure without taking their interconnectivity into consideration. It has long been acknowledged that membrane behaviour of reinforced concrete structures can significantly increase the robustness of a structure and delay a complete collapse. An experimental large-scale test was conducted on a horizontally restrained, continuous reinforced concrete slab exposed to an artificial failure of the central support and subsequent loading until collapse of the specimen. Within this investigation the development of catenary action associated with the formation of large displacements was observed to increase the ultimate load capacity of the specimen significantly. The development of displacements, strains and horizontal forces within this investigation confirmed a load transfer process from an elastic bending mechanism to a tension controlled catenary mechanism. In this contribution a special focus is directed towards strain and crack development at critical sections. The results of this contribution are of particular importance when validating numerical models related to the development of catenary action in concrete slabs