MECHANICAL PROPERTIES OF GYPSUM BOARD AT ELEVATED TEMPERATURES
Gypsum board is a common fire barrier used in house and general building construction. Recently, evaluation of the collapses of the World Trade Center Towers highlighted the potential role and failure of gypsum board in containing the fires and resisting damage. The use of gypsum board as primary fire protection of light-flame wood or steel construction is ubiquitous. Yet knowledge of the common engineering mechanical properties of this construction product is nearly nonexistent. Gypsum board is used in a prescriptive manner with little or no rational design. Summarized here are the results of a study examining the mechanical properties of Type X gypsum board at elevated temperatures. These properties are needed to contemplate the engineering design of gypsum board fire barriers. Tests were undertaken with a small oven within a test machine measuring mass loss, shrinkage, bending strength and modulus of elasticity at elevated temperatures to 400°C. The research showsthat shrinkage and calcination of the gypsum board appear complete between 20 to 30 minutes of exposure at a uniform 400°C. Only after complete calcination, where all moisture is driven off, does the bending strength approach 0. Strength appeared to decrease linearly with increasing temperature. Mass loss and modulus of elasticity exhibited similar trends with the greatest decreases occurring from 100°C to 200°C followed by more gradual decrease to 400°C. The surface paper plays significant stiffening and strengthening roles up to 60 minutes at temperatures as high as 200°C.
NONLINEAR FINITE ELEMENT ANALYSIS OF INSULATED FRP STRENGTHENED REINFORCED CONCRETE COLUMNS SUBJECTED TO FIRE
Recently, Fiber Reinforced Polymers (FRP) have been successfully used for retrofitting or strengthening of existing concrete structural members due to its superior properties such as high strength, corrosion resistance and ease of application. However, its behavior under elevated temperature likely to occur in case of fire is a problem that presents a threat to the strengthened member. This paper presents numerical investigation of reinforced concrete (RC) columns strengthened with FRP and insulated by a thermal resisting coating under service load and fire conditions. The finite element numerical modeling and nonlinear analysis are made using the general purpose software ANSYS 12.1. Numerical modeling is made for FRP-strengthened and insulated RC columns that have been experimentally tested under standard fire tests in the published literature. The obtained numerical results are in good agreement with the experimental ones regarding the temperature distribution and axial deformations. Thus, the presented modeling gives an economic tool to investigate the performance of loaded FRP strengthened columns under high temperatures. Furthermore, the model can be used to design thermal protection layers for FRP strengthened RC columns to satisfy fire resistance requirements specified in building codes and standards.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.