Strengthening of beams or slabs using temperature induction

Abstract

Several aged reinforced concrete (RC) structures need to be strengthened. A typical method is to subsequently add rebar into slots filled with bonding mortar. However, this kind of strengthening only acts for live loads, not for dead loads, if no prestressing or prior lifting is applied. To overcome this deficiency, a novel method is presented. It activates the postinstalled reinforcement for all types of loading by temporarily inducing temperature from the outside. Doing so, statically indeterminate structures are locally relieved from stresses by constraint moments from systematically induced vertical temperature gradients during strengthening. To set the size of the gradients, the nonlinear material behavior, especially the significant reductions in constraint forces due to softening, is taken into account. If tempering is stopped after strengthening, stresses from dead loads redistribute over the newly formed total cross section. The method is theoretically derived, discussed, and verified in the lab on a two‐span RC girder. It turns out appropriate to enhance the bending resistance of beams or slabs.

Scaled concrete beams containing maximum levels of coarse recycled aggregate: Structural verifications for precast‐concrete building applications

“…Based on conventional methods, 60,61 the structural behavior of a beam upon which a point load (or the resulting equivalent load) is applied at the midpoint of its span depends on the quotient between its span and its depth: If the quotient is less than two, it is considered to be a “short shear beam.” Under those circumstances, the shear stress will therefore be much greater than the bending moment, so that the beam will be working exclusively under shear stress and any bending stresses may be disregarded. If the quotient is greater than five, it can be considered that the beam almost behaves to an ideally De Saint Venant beam 62,63 . Under typical load conditions, the bending stress will be much more relevant than the shear stress, and the beam will experience a banding failure if it incorporates a conventional reinforcement.…”

“…• If the quotient is greater than five, it can be considered that the beam almost behaves to an ideally De Saint Venant beam. 62,63 Under typical load conditions, the bending stress will be much more relevant than the shear stress, and the beam will experience a banding failure if it incorporates a conventional reinforcement. The load should therefore be applied at a point close to a beam support when a shear test is performed.…”

Experimentelle und numerische Untersuchungen zu Zwangkräften aus Temperaturdifferenzen

“…Stahlbetonbalken entstehenden Zwangnormalkraft infolge einer Abkühlung. Es sei angemerkt, dass die Tragwerksantwort im Falle einer gezielten Aufbringung von temperaturinduzierten Zwangspannungen auch zur Entlastung des Gesamtsystems genutzt werden kann [12–14].…”

“…Stahlbetonbalken entstehenden Zwangnormalkraft infolge einer Abküh lung. Es sei angemerkt, dass die Tragwerksantwort im Falle einer gezielten Aufbringung von temperaturindu zierten Zwangspannungen auch zur Entlastung des Ge samtsystems genutzt werden kann[12][13][14].Die für die Entwicklung der Zwangkräfte erforderliche Verformungsbehinderung wurde durch einen Stahlrah men erzeugt. Ein nennenswerter Behinderungsgrad ist in solchen Untersuchungen nur mithilfe eines Rahmens mit hoher Biege und Dehnsteifigkeit (vgl.…”

Einfluss einer Wärmebehandlung auf das Verbundkriechen von hochfestem Beton

“…Letztere erfolgt bspw. durch das temporäre Einprägen von Zwangsschnittgrößen infolge einer gezielten Temperierung des Bauteils während der Verstärkung [10][11][12][13]. Alternativ dazu wird derzeit untersucht, nachträgliche Bewehrungen durch Erwärmen thermisch vorzuspannen.…”