This paper investigates the use of structural damping in blast response calculations. In recently published literature, there are many examples of structural damping being used in computational models with little or no experimental or theoretical justification. The use of even small amounts of damping in computational models involving nonlinear plastic response can significantly influence the response calculations. For example, for a given blast loading, a reinforced concrete slab with only 48 kPa maximum capacity and 25 percent of critical damping (a value typically recommended) will deflect the same as (i.e., provide the same level of protection as) a slab with 690 kPa maximum capacity and no damping. Clearly a fictitious damping term that provides as much as 93 percent of the resistance is problematic. Structural damping during plastic response cannot be clearly defined or verified experimentally. Therefore, the use of damping in plastic response calculations should be avoided.

This paper discusses the historical development of design criteria for blast resistant buildings in the petrochemical industry, including static vs. dynamic design requirements for control rooms, and TNT equivalence vs. VCE models for quantifying blast loads. Existing industry guidelines for the siting and design of plant buildings are reviewed. A methodology and examples are presented for the categorization, design and structural evaluation of building components for blast resistance

This paper is concerned with the description and explanation of Hardened Cement Paste (HCP) response to dynamic (explosive) loading. An experimental testing technique had been developed to study the dynamic cracking of HCP samples, using cylindrical explosive microcharges. Following the initiation of the microcharge, radial cracks propagate and measurements of their growth may be conducted. Procedures to predefine the crack path have been investigated, like preparation of linear grooves along the sample. Predefining the crack path enabled relatively simple measurements of its propagation velocity. The dynamic crack propagation velocity was found to be relatively low, within the range of 70-200 m/sec. (about an order of magnitude lower than the theoretical value). The dynamic HCP failure process was found to be usually of multicrack type. Studies of michrocharge initiation near a samples boundary provided insight into the development of scabbing cracks and of their interaction with the radial cracks propagating towards the boundary. It has been found that that crack interaction is strongly dependent on the relationship between the stress wave velocity and the crack propagation velocity.

There are a number of existing facilities at petrochemical plants which : house a significant number of personnel as well as expensive control equipment which must provide protection during an explosion accident. Many of these structures are not capable of resisting blast pressure which may occur during an explosion because they were not designed for these loads. As a result, the potential for significant hazards to personnel and equipment exists at many plants. This paper describes a project involving the scenario postulated above. The existing building was constructed of unreinforced masonry yet was subjected to peak reflected blast loads on the order of 70 psi (483 kPa). A poured-in-place, reinforced concrete box was selected for the new structure. Walls were designed to resist reflected blast loads in flexure and to transmit reactions to the roof diaphragm and shear walls. Walls and roof sections were designed using single-degree-of-freedom (SDOF) methods for determination of dynamic response to the transient blast load. Control conduits extending from the existing walls presented several difficulties for construction of the new walls. A confined working area, high water table, and a requirement for equipment to remain operational also posed unique design challenges.

The mechanical behaviour of concrete is based on the extension of present internal damage, the fracture process. To understand and predict the rate effect on material behaviour, the influence of dynamics on this fracture process should be considered. This idea was followed in the model developed at the TNO Prins Maurits Laboratory (TNO-PML). The damage extension in the real material was represented as crack extension in a fictitious fracture plane using the basic principles of Linear Elastic Fracture Mechanics (LEFM). This resulted in a good model prediction of the dynamic tensile strength, including the steep strength increase at high loading rates. The model clearly shows that inertia effects govern the mechanism of this steep increase. In this paper the various steps in the modeling process are described, specially focusing on the representation of the characteristic internal damage into a fictitious fracture plane. To illustrate the applicability of the approach it is presented in comparison to results of tensile tests with and without lateral compression.