CFRP Composites for Strengthening of Reinforced Concrete Walls with Openings
This paper presents the results of a research work aimed at investigating the potential used of externally bonded Carbon Fiber Reinforced Polymer (CFRP) composite sheets as a strengthening solution for uniaxial rectangular concrete walls with central rectangular in-plane openings. Seventeen of 1/3 scale rectangular concrete walls with and without central rectangular in-plane openings of different sizes (5%, 10%, 20% and 30% of wall areas) are tested. In thickness direction, one central layer of steel fabrics was used to reinforce the concrete walls. The walls were subjected to uniaxial loading aligned with the longest edge of the concrete walls. The loading was applied eccentrically (t/6) with respect to the mid-plane of the walls. Two different patterns were used to fix the CFRP to both surfaces of the walls which are parallel to the midplane of the wall segments. The first pattern consisted of applying four strips of CFRP parallel to the four edges of the opening such that they framed the opening. In the second pattern, CFRP strips were used to reinforce the walls in the vicinity of the opening edges only, i.e. four CFRP strips were applied close to the corners of the openings, in an angle of 45 degrees with both adjacent edges of the opening. From the results of the research work, it was found that CFRP strips applied at an angle of 45 degrees to both adjacent edges of the opening yielded a better compressive strength compared to the CFRP strips that framed the openings. Keywords-Reinforced concrete wall, opening, ultimate load, Carbon Reinforced Polymer, CFRP, stress concentration, strengthening
Ultimate strength of precast concrete sandwich panel with opening under axial load
Saheb and Desayi [3] realised the need for more detailed information on panels with openings. The authors carried out test on twelve panels; six were supported at the top and bottom only and the others were supported on all four sides. Each panel was provided with a window or a wall opening in different regions. The size of the panels was 600mm high x 900mm long and 50mm thick. The test panels were subjected to in-plain vertical loads applied at an eccentricity. The test panels had identical vertical and horizontal reinforcement ratios, i.e., either r = 0.173 or 0.236, and the concrete strength was set at 28 N/mm2. The slenderness ratio i.e. the height to thickness ratio was constant at 12, the thickness ratio at 18, and the aspect ratio at 0.67. To prevent premature failure due to cracking at corners, reinforcement was placed at 45 degrees in these areas. The conclusions to these tests were: 1. The failure of the concrete panels appeared to be due to buckling influenced by bending of slender column strips adjacent to the openings. 2. Empirical equations were developed for panels with openings for both one-way and two-way panels by modifying the ACI formula and the introduction of a reduction parameter that allowed for the geometry of the openings. 3. The panels supported on four sides appeared to be slightly stronger than the one-way panels. The cracking load was marginally greater for panels under two-way action. But more importantly, the ultimate load was found to be nearly equal.
Dating of Historical Manuscripts Using Spectrometric Methods: A Mini-Review
An overview is provided of spectrometric methods useful for age estimation of historical manuscripts (medieval ones in particular), in order to confirm their authenticity. Individual methods (infrared and Raman spectroscopy, mass spectrometry, atomic emission spectroscopy, X-ray spectroscopy, and electron scanning microscopy) are discussed and examples of their application described. The following general strategy can be recommended for dating and/or authenticating of historical manuscripts. First of all, the pigment analysis should be carried out using Raman spectroscopy (distinguishing the period and modern pigments), followed by PIXE ink analysis (solving the question of ink homogeneity). Finally, the radiocarbon dating of the writing support, potentially supplemented by the ink dating using scanning Auger microscopy should be performed.