GB2175036A - Reinforcement of existing roof or floor - Google Patents

Abstract

Auxiliary panels 3 are connected to existing, weakened, beams 1 by stirrups 2 which are bent, while red-hot, round the chord or flange of beam 1. On cooling, the contraction of stirrup 2 causes it to clamp on beam 1. Reinforcement 4 and concrete 5 are then applied. <IMAGE>

Description

SPECIFICATION A process for the post-installation reinforcement of roof or floor structures and for .the restoration of their load-bearing capa city.

The present invention concerns a process for the post-installationn reinforcement of roof or ceiling or floor structures including primarily such structures including steel beam(s) as well as for the post-installation restoration of their load-bearing capacity.

The most widely adopted structures of this type are specified as follows: (a) Reinforced slag concrete structures between steel beams of the 'Mgtrai' system (see Fig. 1).

b) Brick-vaulted roofs between steel beams (see Fig. 2).

The renewal of the aforesaid floor or roof/ceiling structures is accomplished by -demolishing the whole structure and mak ing a new structure from a new material, i.e.

by replacement, -erecting under the old ceiling/roof or floor a new, all-steel construction reinforcement by means of trapezoidal sheets while the old structure remains in place as a load.

Evaluating both of the above, generally-applied methods of renewal we can ascertain the following facts: 1) Renewal of ceiling/roof or floor structures by replacement Advantage: A new, freely designed structure can be erected independently of the old structure.

Drawbacks: -It is necessary for all the ceiling/roof or floor structure to be demolished and removed.

-The demolished materials and constructional elements are entirely wasted, yet they still have a high load-bearing capacity.

-Since the process requires demolition, temporary support or securing, the high live labour requirements as well as the difficulty of mechanisation, the renewal is very time-consuming. In given cases, the renewal of a residential building may take years while the residents have to be evacuated.

-The renewal requires a high amount of material and energy input.

-Inside the building to be renewed there is no possibility for intermittent renewal.

2) Renewal of ceiling/roof or floor structures by means of trapezoidal roofing sheets Advantage: -Inside each building the work can be performed continuously or intermittently.

-As compared to the replacement method, the required amount of demolition work is less.

Drawbacks: -The existing carrying or load-bearing capacity of the old structure cannot be utilized, necessitating an otherwise unjustifiable oversizing of the structure.

-The placement of large and heavy reinforcing steel beams and girders cannot be mechanized, and this requires extremely difficult and heavy physical work.

-In the course of execution, one must proceed with a great care, instal the constructional elements with a high accuracy; demolish, concrete and inject the pockets or nests painstakingly. On this account the possibilities of errors are considerable and they cannot be controlled by simple means.

-The task of anti-corrosive protection of the free-remaining steel constructions cannot be achieved, causing systematic and expensive maintenance work.

The steel structures are unaesthetic for residential buildings, hence an expensive pseudoceiling or floor in each case must be incorporated.

The present invention (defined in the appended claims) seeks to eliminate the aboveenumerated drawbacks and aims to -utilize the advantageous properties of existing constructional elements in order to save material and energy, and -provide a system that may be executed rapidly by structures of statical reliability requiring little or no subsequent maintenance.

The present invention concerns a process for the post-installation reinforcement of, or the restoration of the load-bearing capacity of ceiling/roof structures, wherein the vertical load-bearing structure, the constructional elements of the ceiling/roof or floor, the steel beams and girders, the fields or panels between the beams are examined and are supplemented according to necessity by elements which collaborate with the original structure to complement its load-carrying capacity, whereby to create a collaborative structure suitable for the designed or planned service life.

The methods for the collaborative complementation of the structural parts of the ceiling or roof are specified as follows.

a) Reinforcement of steel beams and girders, represented in Figs. 3 and 4 where the designations are: 1-the steel beams to be reinforced, 2-a clamping stirrup, 3-a complementary girder plate, 4-a reinforcement of slab or panel, 5-an injected concrete slab or panel.

The reduction in cross-section of the existing steel beams caused by the corrosion is compensated or supplemented by complementary girder plates 3 having a predetermined cross-section, at the most critical loci of the stress, i.e. on the drawn girder. The collaboration of the steel beam 1 and of the comple mentary girder plate 3 incorporated additionally is assured by means of the clamping stir rup 2 in such a way that the clamping stirrup 2 is-heated to redness and bent on the chord or flange of the existing steel beam 1 with the complementary girder plate 3 clamped therewith. The clamping force arising under the effect of the contraction in the course of the cooling of the clamping stirrup 2 tightly forged on the plate assures the collaboration of the new tensile complementary girder plate 3 and of the old steel beam.

The nest required for the placement of the clamping stirrup 2 has to be concreted. Injected concrete plates 5 are formed simultaneously with the reinforcement of the panels.

With this sequence of operations the existing and expediently formed beams may be also attached to the new structure to obtain a uniform collaborating construction.

b) Reinforcement of the panels The reinforcement of the panels is required primarily for ground (bearing) concrete which is with or without structural steel section inserts.

Since no simple and reliable method is available for testing the originally incorporated reinforcement, and generally the latter no longer meets current specifications, a new reinforcement is necessary in each case.

It is expedient to form the new tensioned girder of the slab field or panels by means of fastening a steel mesh. The mesh or lattice is fastened to the panels by means of injected pins or rivets and to the reinforced steel beam by means of welding. If the slab fields or panels are made from other materials the procedure has to be applied similarly.

Finally, the new tensioned girder is concreted to the required thickness by an injection method. In addition to the adhesion of the concrete, the above-mentioned and incorporated elements also serve for achieving the collaboration of the slag concrete panel or slab and of the new tensioned girder.

We have carried out experiments as regards the value of the adhesion resistance to be taken into account. The results obtained are summarized below.

The experimental tests were performed on low-quality slag concrete slabs having a strength of 25.5 kp/cm2. The experimental tests have included tests of the adhesive and tensile resistance of the existing slag concrete and of the reinforced concrete panel or slab injected onto it as well as the tests concerning the collaboration of the slag concrete and of the injected reinforced concrete panel/slab due to the adhesion. According to the results of the experiments the characteristic value of the adhesion and tensile strength amounts to 0.0418 N/mm2 (0.418 kg/cm2). This value was evaluated by applying statistical methods.

The results of the breakdown tests performed for the determination of the collaboration characteristics having demonstrated that the slag concrete and the injected concrete were not separated, consequently, one obtained a collaborating construction having satisfactory adhesion. Loading tests perfomed with a predetermined slab width have shown that the improved ceiling or roof structure made from injected concrete by the process of the present invention is capable of carrying a useful load of 250 to 300 kg/m2 in addition to its own load with a high safety of mainte nance, which value is in excess of the loading required for dwelling houses.

An advantage of the invention consists in the possibility of prolonging the life of ceiling/roof structures to the design length by util izing the strength properties of the old structure which still exists and can still be relied on.

By utilizing the advantageous properties of the old structure material, energy and live labour may be saved.

The materials incorporated for complementing the load-bearing capacity can be applied in a much more economic manner than is the case when erecting a new ceiling/roof or floor structure.

The human labour required for the execution of the works is only a fraction of that required for a replacement of the ceiling/roof or floor and it is lower than that required in the trapezoidal-plate constructional technique.

The construction erected in this way has no need for special or separate anti-corrosive protection treatment. The surface can be loaded, covered or faced and shaped as desired.

The process may be mechanized to a high degree. The constructional works do not require any expensive auxiliary structure (scaffolding, etc.) or a long period of execution.

In the cae of a dwelling house, it is not necessary to evacuate it completely during the works.

The advantages of monolithic structures can be fully exploited at the planning stage without the necessity of special shuttering.

The product made by the process is readily marketable.

Claims (3)

1. A process for the in-situ reinforcement or renewal of corroded or decayed roof or floor structures comprising examining a) the load-bearing capacity of the vertical load-bearing structures associated with said roof or floor structures, b) the elements of said roof or floor structures, e.g. steel beams and girders, and c) the statical condition of the slabs, panels and other elements between the beams and girders, and preparing a load-bearing structure co-operating with the elements of the original structures by coupling tensile beam flanges in the most loaded regions in previously prepared pockets or nests with a supplementary flange plate and a heated stirrup whereby to utilise the shrinkage/contraction forces on cooling of said stirrup, securing the thus reinforced beam in place, securing a metallic mesh to the panels or slabs of the roof or floor structure, filling the said pockets or nests with injected concrete, and covering the interstices of the structural elements and the said mesh with injected concrete.

2. A process according to claim 1, wherein the said mesh is secured to the existing roof/floor slab by bolts or pins or the like, and is expediently welded to the existing or supplementary flange plate, then covering the mesh with injected concrete to increase the structural co-operation of the mesh by the adhesive force of the concrete.

3. A process for the in-situ reinforcement or renewal of corroded or decayed roof or floor structures, substantially as herein described with reference to and as shown in Fig.

3 and/or Fig. 4 of the accompanying drawings.