Thermal stress analysis with inclusion of fracture mechanics. Analysis of internal stresses in HSC elements, caused either by thermal stresses or pore pressure buildup, with consideration of other factors such as creep and shrinkage, must be made in order to determine the relative importance of thermal stresses and pore pressure on the tendency for spalling. A fracture mechanic approach may be needed. (4) Coupling of pore pressure andfi-acture process. Accurately measuring and predicting pore pressure buildup during a fire situation is not enough. Experimental data showing that pore pressure does not drop to zero when a crack forms led to a new approach in analyzing the initiation of spalling. Thus modeling to predict spalling should include the effect of cracking and interaction between the pore pressure and the crack. Codes and Standards (1) Standard Test Protocols for Engineering Properties of Fire-Exposed HSC. Internationally accepted protocols for fire testing of HSC, which include guidelines for data collection and reporting, need to be developed to ensure compatibility of results from different test programs. (2) Mechanical Properties-Temperature Design Curves for HSC. Existing design curves for estimating mechanical properties of fire-exposed concrete have been developed based on experimental data of NSC. These design curves have been shown to be unconservative when applied to HSC. Thus, mechanical properties-temperature design curves for HSC at high temperature need to be developed and incorporated into building codes to ensure safety in HSC structures in the event of a fire. Such design curves would also be helpful for assessing the residual strength of HSC structures after a fire. (3) Guidelines for Interpretation of HSC Material Tests and Standard Fire Tests. Engineering properties of HSC at elevated temperature are obtained by testing HSC cylinders or prisms. The measured properties are typically related to the temperature measured at the center of the specimens and are dependent on, among other things, heating rate. Whereas the current standard fire tests, such as ASTM E 119 and ASTM E 1529, prescribe procedures for testing structural assemblies by subjecting them to standard ambient temperature-time histories. These standards characterize the temperature history and duration of exposure inside the test chamber, but not necessarily the temperature and the rate of temperature development within the assemblies. Thus the results of material and standard tests are not directly compatible. Guidelines should be developed to relate the results of these tests. (4) Guidelines for Selecting Realistic Design Fire Exposures. Current standard fire exposures, prescribed by ASTM E 119 and E 1529, ISO 834, and JIS A 1304, do not represent likely temperature histories of real fires. As a result, the exposure conditions specified in these standard fire test methods are not necessarily representative of the conditions that may exist in real fire scenarios. With the current tendency of moving towards performance-based ...
