Pathological Analysis of Suspension Corridor and Floor Structures of Residential Buildings

Bukovics, A. Széchenyi István University Győr

(email: bukovics@sze.hu)

Abstract

Load bearing structure was studied in case of more than 340 old residential buildings in Budapest on the basis of building structure and building diagnostic aspects. Conclusions drawn from the examination of the structures of suspension corridors and floors are described in this article. Considering that a significant part of the residential buildings of the inner districts of Budapest are of the similar age, structural system and conditions, the conclusions that can be drawn from this study, may provide valuable information relating to the featuring construction methods of the relevant era and the typical building failures thereof.

Keywords: building diagnostics, building pathology, floor, slab structure, suspension corridor structure

434

1. Introduction

The expert opinion prepared on more than 340 buildings in one of the districts of Budapest has been studied over the last time period. The buildings under review were characteristically built between 1880 and 1950.

Since a considerable part of all of the buildings of Budapest (especially in the inner districts) were built during this time period, and are of similar age, structural design and condition, too, the defects, damages and the conclusions drawn therefrom are of general scope. [1]

“Since over the past decade necessary maintenance and renovation works of buildings have not been performed – mainly due to lack of sufficient funds – this lead unfortunately to the extensive and rapid deterioration of the condition of older buildings.” [2]

Based on the inspection of buildings we can draw conclusions with regard to the characteristic construction methods and the typical construction errors of the given time period. It is our experience that the defects of buildings have not always been repaired in the appropriate manner, thus further damages of buildings, that are due to inadequate repairs, could be prevented by more prudent maintenance and renovation works of the similar buildings.

The results of this research may facilitate to implement the ideas of rehabilitation of the given parts of the town, and can be well applied in the course of the utilisation and renovation of buildings which are in poor condition, too.

Thus considerable financial savings could be achieved by performing the repair of damages in a professional manner and by eliminating any errors during operation. Findings and conclusions made on the basis of the study of the above buildings may be helpful in the optimum utilisation of economical opportunities.

Primarily main load bearing structures (foundation structures, wall structures, suspension corridor structures, floor and roof structures) have been in the focus of my studies. [3] [4] In this lecture the results of the studies of corridor structures and slab structures will be described.

2. Examination method

Examinations have been performed on the one part pursuant to criteria for the structure of buildings, and for diagnostics of buildings, on the other part. Buildings can be typically classified into 3 groups. The first one is the group of multi-storey buildings with 2 to 5 floors. The second one is the group of one-storied buildings, which are in relatively good condition. Third group includes one-storied buildings, which are in bad condition.

435

The above buildings have been studied by groups and jointly, all of them, too. Connections between the detected defects of buildings as well as the structure and materials of the buildings have been sought. The most important statistics and connections have been demonstrated in diagrams and figures.

3. Investigation of suspension corridor structures

Suspension corridors became prevailing in Hungary at the end of the 19th century, when – basically in Budapest –lots of multi-storey residential buildings were built. Although these days the central corridor design has been applied in case of a significant part of multi-storey residential buildings to access the flats, in certain periods of the 19th and 20th centuries the suspension corridor design was nearly exclusively applied to access the flats, and since a considerable part of these residential buildings still exists, it is inevitable to analyse and study them for building diagnostics and building structure in the interest of economical sustainability of such structures.

Suspension corridors were typically built with three different types of structural systems: with steel brackets (58%), stone brackets (24%), and monolithic reinforced concrete plates. Suspension corridors built with steel brackets have been made with reinforced concrete plates (51%), Prussian vault (26%), cinder concrete plates (MATRAI) (16%) and natural stone plates (7%) alike. Suspension corridors built with stone brackets are covered by natural stone plates (46%), monolithic reinforced concrete plates (47%) and precast concrete plates (7%). [Figure 1]

Figure 1: Apportionment of structures of suspension corridors in case of buildings under review

In the case of the investigated suspension corridors the allocation of axis of brackets ranges between 0.90 and 2.40 m. Fixing within the brickwork has been implemented by loading or anchorage.

The plate structure of steel and stone bracket type suspension corridors is nearly exclusively of the single span support design in case of cinder concrete, natural stone and prefabricated reinforced

436

concrete plates. If monolithic reinforced concrete materials are used for the plate structure, it can be of single span plate or continuous plate according to its static frame. In case of single span design the reinforced concrete plate is arranged between the bottom and the top flange of the steel beams, and the plate is supported by bottom member. In case of continuous slab design two general structures were used. In the first case the bottom reinforcement rod is of the single span plate design, and is arranged between the steel beams, and the top reinforcement rod is of the continuous plate design arranged over the steel beam. In the second case the reinforced concrete plate is placed over the steel beams, and the bottom and the top reinforcement rod is of the continuous design alike.

In case of the majority of suspension corridors constructed with monolithic reinforced concrete one side of the slab is restrained into the reinforced concrete ring beam in its entire width. The stability is ensured by the weight of the brickwork over the slab.

Typically steel bracket type suspension corridors were built between 1890 and 1920, the monolithic reinforced concrete plates became widespread as from the 1930s. In case of the examined building stock stone brackets were used in all of the construction periods. [Figure 2.]

Figure 2: Changes of the material of suspension corridors in case of buildings under review

The most frequently occurring defects of the monolithic reinforced concrete plate type suspension corridors are the frost damage (43%), cracks of the slab plate (17%) and corrosion of the reinforcement rod (13%). A frequently occurring defect of the steel brackets is the corrosion of steel beams (spal).

Common mistake made during the construction of suspension corridors was the lack of providing an adequate slope required for drainage, thereby causing constant soaking of flats in the line of perimeter walls. A considerable part of the suspension corridors in the older condominium houses in Pest is in very bad condition.

437

To ensure safe usage, 24 % of the analysed suspension corridors were strutted. Unprofessional strutting has caused the deterioration of wall and slab structures in many cases. Strutting was erected to high in many cases, as a consequence whereof storm-water and slush was flowing down towards the wall, making them wet, thereby causing deterioration, many often the peel off of the plaster. In case of timber slabs wetting occurs at the place where the joists are the most sensitive to wetting, that is at the tailing thereof. Water-drenched beams may get rotted, as a result whereof entire slab sections may be exposed to the direct risk of collapse. [Figure 3.] It has often occurred that strutting has reduced the width of suspension corridors to such a great extent that prevented traffic there.

Figure 3: Flowchart of structural damages of suspension corridors caused by inadequate slope

In case of those suspension corridors, which were made with Prussian vault brickwork between the steel beams using larger size bricks it was a frequently made mistake that the Prussian vault brickwork was made without padding, bending and arch, as well as with irregular brick bonds.

In case of suspension corridors with stone plate structure, supported by stone brackets it is a frequently made construction error that the natural stone is plastered. As a result of the natural process of the “breathing” of natural stone the Tyrolean plaster of rock flour has peeled off locally from the bottom plane of the stone plate of suspension corridor of several buildings.

4. Investigation of floor structures

Floor is one of the most important load bearing structure of a building. It is intended to transfer the loading to the walls and the lintol beams. Based on their location the floors can differ within one

438

building, too. This is why the cellar floor, the intermediate floor and the cover floor have been separately studied.

In case of cellar floors the steel beam type floors were the most frequently used ones. (48%). Basically they were prepared by brick vault (37%), but reinforced concrete or Horcsik slab was also frequently used. (8%) Another frequently used floor type was the use of vaults, but bottom or top ribbed monolithic reinforced concrete slab was also often used (9%) (generally Portland cement, but rarely bauxite cement was used). [Figure 4.]

Figure 4: Apportionment of structures of cellar slabs

Vaults have primarily built between 1880 and 1910, thereafter their use has significantly decreased. Steel-beam type floors were typically built during the time period between 1890 and 1930, the application of monolithic reinforced concrete slabs started around 1920. Monolithic slabs with brick profile were solely built in the 1920s. [Figure 5.]

Figure 5: Changes of the material of cellar floors in terms of time in case of buildings under review

439

Also in case of intermediate floors the steel beam type floor occurred the most frequently (70%). Typically brick vault (54%), reinforced concrete or Horcsik slab (9%) was placed between the steel beams. 12 % of the floors was made of bottom or top ribbed monolithic reinforced concrete (using Portland cement or bauxite cement), and 9-9 % of floors was made of precast reinforced concrete beams (with brick vault, reinforced concrete or Horcsik slab, prefabricated concrete or reinforced concrete element), and of timber. [Figure 6.]

Figure 6: Apportionment of structures of intermediate floors

Steel-beam floors became widely used around the turn of the century, while wooden floors were only made up to 1890. Monolithic reinforced concrete plates were basically built from 1930. [Figure 7.]

Figure 7: Changes of the material of intermediate slabs in term of time

440

The cover floors were predominantly (92 %) built with wooden structure, and a smaller portion (4 %) with monolithic reinforced concrete slabs. Any other floor structures seldom occur in the case of cover floors.

In the case of floors built with steel beams the most frequently occurring defects of the cellar floors and intermediate floors is the corrosion of steel beams, while in the case of reinforced concrete plates it is the corrosion of the reinforcement rod occurring due to the imperfect concrete cover for reinforcement. 42 % of bottom or top ribbed monolithic reinforced concrete slabs was prepared using bauxite cement, which is exposed to considerable decrease of strength in an area with high moisture content and due to high temperature. The cinder concrete slab structure (Matrai-slab) between steel beams is very sensitive to moisture. If exposed to moisture, vitriol and the derivatives thereof may be produced, which may cause corrosion of reinforcement rod and the steel beams.

Frequently occurring damage of the cover floors are the rot (43%), fungal infections (27%), soaking (20%), and infestation (18%). 20% of the floor beams are cracked and 20% thereof has deflection exceeding the allowable limit. 7 % of the beam ends, supported by walls underneath, are not insulated, which may result in the rot of the beam ends, exposed to accident risk. [Figure 8.]

With steel beam floor with Prussian vaults cracking occurred in the entire length parallel to the direction of load-bearing. In such cases the floor section peeled off from the steel beam due to the outbound dislocation of the support of vaulted section (e.g. end-wall of the wing).

It is a frequent damage of steel beam floor with reinforced concrete slabs that the reinforced concrete slab elements get loosened from the flange of the beam. In general it happens as a consequence of the movement of buildings. As a consequence of further movements of buildings the floor may become dangerous to life due to smaller support of the slab sections.

Figure 8: Frequency of cover floor failures in case of buildings under review

441

On steel beam floor with pinned timber beam elements typically the following deteriorations could be observed: Floor surface is uneven due to the slackening of the pinned beam floor sections. Beams, which got totally damaged at the support section, are only held by the structural fixation. As a result of the slackened timber beams, majority of the steel support beams is twisted and bent down.

It is a typical and extremely dangerous defect of pinned timber beam floors when the signs of initial rotting are detected on the un-insulated beam ends. Generally it occurs due to leakage. It is especially dangerous because apparently the floor is not bent and it can even totally sound. The defect can only be diagnosed by detection.

The pinned timber beam floor of one of the investigated building has broken down and became life-threatening. Beam-ends at the main wall support were not insulated. In the course of detection if was found that most of the beam ends got rotten at the main walls. Floor was supported only by pinning together the still upward leaning beams! Under such conditions the slab could have torn away at any time! (The solution was the total replacement of the floor)

In many cases the covered beam floors (sawn pine beam, covered with board, with sand and slag filling) have bent down to a large extent, which, after a while, may cause the total deterioration of the floor, too. In the case of this type of deterioration of floors, typically two methods were used to alleviate the deterioration of the floor. In one case the loading, thereby deformations were decreased by removing the filling at the loft section. In the other case framed strutting was used in the central section to reduce the span.

If, in the course of the renovation of covered timber beam floors, due to the construction water the top boarding gets stuffy, and cannot be aired thoroughly, rotting and fungous decay processes will start, which means the natural deterioration of the wood, which got stuffy and cannot be aired. It has occurred with the covered timber beam floor of several building, that certain portion of the covering has fallen down through the gaps of the top boarding onto the bottom boarding, thereby exerting direct loading on the boarding as a result of which the bottom plane of the floor has become seriously cracked and bent inwards. In case of the covered timber beam type cover slab it may occur that leakage in the roof will attack the boarding by washing away the slag filling.

In case of some buildings horizontal power effects have been generated due to the defective fixation of the roof structure, as a consequence whereof the attic wall directly loaded by the roof structure, bent outwards, and horizontal cracks have appeared in the entire length of the plane of the floor. Deflection of floors, exceeding the allowable limit, has occurred at various places, irrespective of the materials and structural system.

5. Conclusion

Deteriorations of the horizontal load-bearing structures (floors, suspension corridors) of the old residential buildings can be more dangerous than those of the vertical load-bearing structures. On the one hand it is partly due to that these structural elements are significantly more sensitive than e.g.

442

foundations or wall structures, on the other hand that severe deteriorations remain hidden and very often can only be diagnosed in case of detection. Connections can be detected between the age, structural system, material and the diagnosed construction defects of the buildings.

A considerable part of the current residential buildings of Budapest were build at the end of the 19th century or beginning of 20th century, therefore regular supervision and in the case of necessity the renovation thereof is vital.

Inefficient renovations or maintenance interventions very often cause more damages than benefits, and even the main load bearing structures, which were in acceptable condition, can be deteriorated to a large extent (e.g. excessive lifting of suspension corridors with strutting)

References

[1] Preisich G (2004) History of Town-planning of Budapest from the Battle of Buda till the Second World War, Budapest, TERC.

[2] Koppány A (2000) Building diagnostic – Construction defects – Building pathology, Budapest, Magyar építőipar 2000. 11-12. p: 341-350

[3] Bukovics Á (2009) Structural and diagnostic analysis of residental houses in Budapest – Part 2 Insulations, wall- and outside corridor structures, Budapest, Magyar építőipar 2009. 2. p: 58-61.

[4] Bukovics Á (2009) Structural and diagnostic analysis of residental houses in Budapest – Part 3 Floor structures and roof structures, Budapest, Magyar építőipar 2009. 3. p: 87-90.

443