Reliable analitical methods are needed to aid the analysis and design of concrete structures under impact and blast loading. Calculated results from such an analysis are often compared and fitted with physical test results to validate the method of analysis employed. Material models used in the analysis must, account for strain-rate sensitive behavior, and these material models are also based on results from experiments. Hence, reliable development of material models and analytical techniques is contingent upon correct, observation of experimental results. This paper focuses on effects which could alter the test results and influence their subsequent interpretation, such as testing machine characteristics, inertia, time delays in measured signals caused be analogue filters, and vibrational energy. All of these effects can lead to incorrect, measurement of a test response under high strain-rate loading. Examples are given of incorrect measurement, of the compressive stress-strain response of concrete at strain-rates in the order of 0.1 s -1 , where results from such tests have been obtained with hydraulic testing machines. Failure to account. for inadequacies in the testing technique affected conclusions about changes in deformation behavior (such as stiffness and axial strain at peak stress). and also led to an apparent loss of ductility. Results from impact tests on a flexural member demonstrate how vibrational effects from a falling mass can lead to incorrect conclusions about the measured contact. load.

Nuclear newer plant structures, systems and I components may be subject to a variety of impulsive loads caused by accidental explosions and or high energy pipe ruptures. Examples of such loads are jet impingement, reactor vessel sub-compartment pressurization, pipe whip restraint reaction and blast pressure. Various US NRC Regulatory Guides and Standard Review Plans specify required loads and provide acceptable methods for structural design. The design of concrete structures, subject to impulse and impact loads is governed by the ACI-349 Code. Acceptable analysis techniques vary from simplified quasi-static methods for single degree of freedom systems, to detailed computer analysis techniques accounting for material and geometric non-linearities. This paper reviews briefly the impulsive loads and the procedures for analyzing a n d designing structures found in nuclear facilities.

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.

The 15 papers in this Symposium Publication describe a range of applications for this seemingly narrow area of structural engineering: design to resist or discourage terrorism against civilian and governmental buildings, design to eliminate or minimize destruction from industrial accidents, and design to protect military facilities. To assist the reader in focusing on a particular level of interest, the papers have been grouped into three sections. Section One, Design Aspects, relates directly to the design process. Section Two, Current Procedures and Recent Developments, provides an overall viewpoint. Section Three, Theoretical Developments, focuses on research issues. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP175

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.