Static analysis of bond between prestressing strand and UHPC exposed to elevated temperatures

This article deals with the numerical analysis of the bond of a prestressing strand with UHPC heated to elevated temperatures and subsequently cooled. Numerical analysis was performed with experimentally determined material properties of UHPC at a reference temperature of 20 °C and further after heating to temperatures of 200, 400 and 600 °C and subsequent annealing to normal temperature. The resulting deflection depending on the pulling force from the numerical analysis were compared with the experimental results. The results are used to configure the cement composite model for more demanding simulations of structures and load cases.

The Behavior of a Strengthened Steel Beam Section Under Eccentric Loadings

Thirteen simply supported steel samples have been tested to explain the effects of strengthening steel beams using an external prestressing strand. The samples have the same cross-sectional dimensions and overall length. One steel beam without strengthening was taken as a reference, while the other twelve of them had been strengthening by two external strands at various eccentricity locations and jacking stresses. The strengthening by external prestressing strands is sub-divided into two series according to jacking stress. Each series consists of six steel samples divided according to the eccentricity location of prestressing strand. During tests, it was found that the Load deflection response for the strengthened samples is stiffer as compared with the reference. The increasing percentage in ultimate load capacity was increased to 0.347, 2.758, 3.921, 8.898, 9.326, and 10.256% for beams under jacking stress of 1120 MPa, while increasing percentage in ultimate load capacity were increased to 0.17, 26, 33, 48.5, 13.7, and 69.56% for beams under jacking stress of 815 MPa. On the other hand, the maximum percentages of deflection were decreased to 4.88, 2.44, 20.62, 15, and 9.7% when the jacking stress increase from 815 to 1120 MPa and the ratio of the quarter to mid-span deflection (δ quarter / δ mid) is about 0.528 and 0.497 when jacking stress is 1120 and 815 MPa respectively. So, the increase in jacking stresses from 815 to 1120 MPa will not be preferable because it has a little increasing percentage in stiffening and behaviors compared with other tested beams at the same condition.

Background for the new PCI recommended practice on strand bond

The new PCI “Recommended Practice to Assess and Control Strand/Concrete Bonding Properties of ASTM A416 Prestressing Strand” specifies two new threshold limits for pullout tests conforming to ASTM A416 and new equations for the transfer and development length of prestressing strand. This article provides a summary of more than 30 years of research and knowledge advancement on the bond between concrete and prestressing strand related to the development of the new recommended practice. Discussions regarding the adoption and incorporation of the new recommended practice into structural design, strand production, and precast concrete fabrication and quality control practices are ongoing.

Strengthening of I-Section Steel Beams by Prestressing Strands

Six I-section steel beams had been fabricated and tested to understand the influence of prestressing strand on the load deflection behavior of steel beam. All tested beams are simply supported having the same gross sectional area with clear span (2850) mm, five beams strengthened by two low relaxation seven wire strands, while sixth beam is the reference one. The strengthening beams were subjected jacking stress equal to (1120MPa) and subdivided according to prestressing strand positions (eccentricity). From the experimental tests, it can be noted that, the load deflection curves for strengthened beams are stiffer as compared with reference beam and the percentage of ductility for strengthened beams were decreased when the eccentricity positions change form (0 to 96)mm respectively, on the other hand, the percentage of increasing in maximum applied load for strengthened beams were increased with increasing of strands eccentricity and the maximum applied load reaches to 61.74% as compared with reference, also, the percentage increasing in maximum deflection at middle span for strengthened beams decreases with increasing of strands eccentricity and the minimum percentage of decreasing at middle span of strengthened specimens reaches to 36.31% as compared with the reference beam.