Load testing to determine ultimate loads

(Experimental assessment of load-bearing reliability)



The problem often arises during conversions or renovations that the new loads to be accommodated (e.g. for a change of use) are significantly higher than the original loads. This can result in the calculated influence lines no longer being fully covered, or in a relatively high degree of deflection (fitness for purpose!). The load-bearing capacity of the construction can then no longer be verified through calculation. As a consequence, the components are either strengthened or completely removed and replaced with new ones. This process is very time-consuming and expensive. Load testing can eliminate the need for these conversion measures by verifying the load-bearing capacity of the construction experimentally.


More information about test loading

More information about test loading

More information about test loading

Over the years, the team at MFPA Leipzig GmbH have had the opportunity to gain a wealth of experience in test loading. Their combination of theoretical knowledge and practical experience in this field is virtually unrivalled. Nevertheless, every test presents our team with a new challenge.


In contrast to a calculation model, testing has the advantage that it does not involve making any assumptions about the structure and material. The material model has the additional advantage of addressing spatial load transfer and the actual strength of the material. Supporting floor structures or low tensile strength are likewise not taken into account in a calculation. In the case of load testing, these are included in the ultimate load reserves.


Alongside the reduced cost, the other great benefit of test loading is the time saving. After a determined preparation phase, the tests are carried out promptly. The result of the test loading is available immediately after the tests, leaving the client and planner safe in the knowledge that the existing construction is fit to support the future load.


Load testing is a non-destructive test procedure and is carried out in line with the Load Testing of Concrete Structures guidelines issued by the DAfStb (German Committee for Reinforced Concrete). The target test loads are determined in relation to the new loads to be supported by multiplying the load components by the predetermined load factors. The loads are applied in a minimum of four load stages. The reaction of the component is measured, displayed and evaluated online. The load deformation behaviour must satisfy the deformation criteria set out in the above DAfStb guidelines. These criteria ensure that there is no damage to the test object and guarantee fitness for the intended use.


We also have a load vehicle for testing bridges with a span of up to 18 m, which can be used to experimentally verify the load-bearing reliability of bridges that have already suffered damage, for example.


The online display of the active forces and the resulting deformations means that a judgement on the load-bearing capacity of a particular component can be made immediately after the test loading.


Our services

Our services

Our services

  • Site visit and drawing up a non-binding fixed-price offer
  • All necessary preliminary material investigations (cores, locating reinforcements, characteristic properties of reinforcements, etc.)
  • Inspection of documents, calculation of target and limit loads for non-destructive load testing, calculations and concept for transferring the reaction loads to the structure
  • Formulation of abort conditions to protect the existing components and agreeing these with the structural testing engineer/the relevant building inspection authority
  • Preparation for testing (configuration of measurement equipment, adjustment of the load frame, selection and configuration of the hydraulic load design)
  • Set-up and adjustment of measuring and test equipment on-site, application of bracings
  • Performing test loading including force and deformation measurements with online display, continuous data capture and storage
  • Drafting a test report with graphical display and evaluation of test results, photo documentation
  • Assessment of the validity of the results for adjacent components

References

References

References

Over recent years, the Experimental Structural Mechanics working group at MFPA Leipzig GmbH have carried out test loading on a range of structures. A few of these projects are presented below.


B&B in Bad Aibling

  • Type of property: Accommodation building in a former barracks
  • Component tested: Several upper floors
  • Reason: Change of use

The change of use of the accommodation building of the former barracks into a bed & breakfast made it necessary to increase the working load to be supported by the existing composite floor. These loads could not be verified through calculation. Load tests were therefore carried out on the upper storeys.


Swimming pool building in Dresden

  • Type of property: Public building
  • Component tested: Suspended roof
  • Reason: To determine safety in use for a further 30 years

After 40 years of use, the plan is for the swimming pool building to be used for a further 30 years. It therefore needed to be brought up to the appropriate technical standard. This requires the construction of the pool building to allow for sufficiently long-term and safe use.


From the top edge of the floor, the building is made entirely of prefabricated parts. The main load-bearing elements are the prestressed cable suspension shell, the edge beams, trestles and the foundations. Together these form a load-bearing system; the type and condition of the bonding elements are decisive factors in its effectiveness.


In order to identify any damage or defects in the bonding elements, load tests were conducted on the roof construction. Since the roof construction is curved in shape, the loads could not be generated in the conventional manner. Specially manufactured hoses that adapted to the shape of the roof were filled with water. This represented a major challenge for our team, for which we found an excellent solution.


High school in Bad-Neustadt

  • Type of property: School
  • Component tested: Upper floors
  • Reason: Updated load requirements in DIN 1055-3:2006

The ceilings of the high school are what are known as Monofer surfaces. These prefabricated, prestressed concrete structures are composed of a prestressed concrete bottom chord and a T-shaped reinforced concrete chord/flange system with a compressed concrete layer. The two parts are connected by means of open-web joists, in the same way as a filigree floor. The hollow blocks act as the shuttering here.


According to the ceiling system approval certificate, the in situ concrete layer is 4 cm. Testing the concrete resulted in a strength class of C16/20. This is unacceptable for prestressed concrete. The load also needed to be adjusted to the requirements of the new DIN 1055 Part 3, issued in 2006. The load-bearing capacity of the prestressed concrete floors therefore needed to be tested.


Industrial building in Wernigerode

  • Type of property: Industrial production hall
  • Component tested: Ceiling structure of the basement level (built circa 1938)
  • Reason: Damage to the load-bearing construction

Hall II of VEM motors GmbH in Wernigerode needed to be renovated for renewed use. It had been empty since the beginning of the 1990s, and from that time it had been exposed to climatic conditions with very little protection.


The most important aspect in terms of continued use was the load-bearing capacity of the basement ceiling structure. As no construction documents were available for the monolithic reinforced concrete building (built circa 1938), a series of processes were performed to uncover reinforcement elements in order to determine their layout and cross-sections. These could then be used as a basis for recalculations, although these were only valid for evidently healthy areas of the basement ceiling.


Since, for these areas too, the transfer depth extends into the concrete beyond the outer reinforcement layers, there was also the possibility of loss of strength in the concrete and rust in the steel, meaning that faults in the bond could also occur. Damage of this type cannot be determined through calculation, so the decision was taken to perform an experimental evaluation of the load-bearing reliability. 


Former barracks in Würzburg

  • Type of property: Public building
  • Component tested: Several upper floors
  • Reason: Change of use

Eight four-storey buildings of Leighton Barracks in Würzburg, previously used as living quarters by the US army, were to be repurposed as offices, seminar rooms and lecture halls by the university. In general, this means increased loads on the floors and walls. As no structural engineering design documents survived from the time of building (in the 1950s), this meant that the load-bearing system and its condition needed to be meticulously investigated and a recalculation performed.


Extensive analyses of the condition showed that the ceiling structures were ribbed reinforced concrete slabs, prestressed along one axis and extending over the central wall, having perforated bricks and solid concrete strips in the bearing regions in the central wall. The recalculation indicated that the existing cross-section was exceeded by less than 20%.


In contrast to the calculation model, an experimental assessment of the load-bearing reliability therefore had a good chance of being successful by making use of any existing ultimate load reserves in the real model, i.e. in the principal design. In particular, a test would take account of the actual stiffness present in the load-bearing system and the load transfer in the transverse direction, i.e. the slab action and restraints within the bearing regions. This is not readily achievable through calculation.


Neues Schloss primary school in Neustadt an der Aisch

  • Type of property: School
  • Component tested: Several upper floors
  • Reason: Updated load requirements in DIN 1055-3:2006

The building, constructed around 100 years ago, is currently used as a school and needed renovation. The loads therefore needed to be adapted to meet the new DIN 1055 issued in 2006. With the new loads, the load-bearing capacity of the ceiling structures was no longer sufficient.


In addition, there was known to be damage to the construction caused by temperature stresses, and these could not be included in static verification. A total of four ceiling structures were therefore investigated. One of these was in the corridor area, with a maximum load of 5 kN/m², and the other three were in classrooms, each with a load of 3 kN/m² and spans of up to 7.00 m.


King Albert Museum, Chemnitz

  • Type of property: Public building
  • Component tested: Ceiling structure above the 1st floor
  • Reason: Conversion work

Following conversion work, archives and a library were to be housed in the rooms on the 2nd floor. This meant that the ceiling structure in question needed to withstand a payload of 5 kN/m².


Since it was not feasible to carry out verification by calculation – these are Koenen arched ceilings – load tests were designed and performed. Following appropriate preliminary investigations, the two end spans of the ceiling system, which clearly extended over two interior walls, were selected. We worked with sufficiently wide load strips so that, in addition to the maximum field loading, the load transfer in the transverse direction as a uniformly distributed half-load could also be recorded. Since drilling into the ceiling was not permitted, the reaction forces occurring during the test were derived from the wall, ceiling and roof loads of the top floor.


Weinhold building, Chemnitz University of Technology

  • Type of property: University
  • Components tested: Prefabricated floor beams
  • Reason: Cracks in the bearing region of the floor beams 

At 140 mm on supports measuring just 300 mm in width, the bearing surface of the 7.20 m double beams of 2.0 Mp construction was relatively small. Tolerances resulting from prefabricated part dimensions and installation, inadequately filled bed joints and damaged column edges on the bearing cross-section meant that in many cases the bearing depth was even smaller. This led to the formation of numerous cracks in the bearing region.


By carrying out load tests at selected investigation points, MFPA Leipzig GmbH was able to ascertain the load-bearing reliability and fitness for purpose of the beams. No widening of the cracks was observed. The results indicated that the cracks discovered (with the exception of the spalling on the end faces) did not run through the entire cross-section.


Former Schocken department store in Chemnitz

  • Type of property: Department store
  • Components tested: Several upper floors and floor beams
  • Reason: Increased load caused by change of use; poorly filled ribs

The ceiling structures in the former Schocken department store were continuous Ackermann ceilings with span lengths of 6.60 m. In the support region of the structure, the ceiling blocks had been replaced with solid concrete, meaning that the arched frame girders had a beam-and-slab cross-section. The construction had already been calculated to be suitable for a payload of 5.0 kN/m².


Following renovation, the building was to be a museum, so it needed to be tested for a payload of 6.0 kN/m². The ribs in the Ackermann ceiling were not densely filled, resulting in a loss of adhesion. Load tests were therefore used to verify the construction’s load-bearing reliability and fitness for purpose.


City library, Leipzig

  • Type of property: Library, former museum
  • Components tested: Several upper floors and floor beams
  • Reason: Verification by calculation not possible

For certain areas of the former Grassi Museum, it was not possible to verify the load-bearing reliability and fitness for purpose of the ceiling structures and floor beams by means of calculation. The decision was therefore taken to commission MFPA Leipzig GmbH to carry out load tests.


The regions investigated were pure reinforced concrete ceilings, resting on reinforced concrete floor beams with a span length of up to 7.20 m. By carrying out a total of 16 load tests, MFPA Leipzig GmbH was able to provide the necessary verifications.


Chemnitz regional tax office

  • Type of property: Courtyard above a basement
  • Components tested: Ceiling structure and floor beams
  • Reason: Road surface for trucks up to 16 tonnes

The 20 cm thick reinforced concrete structure with span lengths of 6.00 m were dimensioned according to the standards at the time of building in the 1960s for trucks up to 7.5 t and LKW 15 fire engines. After 40 years of use, there was found to be moisture penetration in large areas of the unfinished slab and structure, leading to fears that the reinforcements could be damaged by corrosion, impairing the load-bearing capacity. Traffic load was thus reduced to vehicles up to 2.5 t.


It needed to be possible for trucks weighing up to 16 t to use the parking area and to access to the entrance ramp safely. In order to determine whether the moisture penetration had had any impact on the structure, load tests were carried out on the slabs and floor beams.


Educational centre, Lutherstadt, Wittenberg

  • Type of property: Public building
  • Components tested:Several floors and floor beams
  • Reason: Change of use (setting up a library)

The building on the corner of Zimmermann and Falkstraße, which had previously primarily been used as a school, was to be repurposed. In future, it would be used by the network Bildung und Kultur (education and culture), with facilities including a regional media office and music school.


Owing to the current regulations and structural engineering requirements, it was not possible to verify the ceiling structures and floor beams by calculation. For example, the building had no load distribution irons in the compressed concrete layer in the ceiling structures, and no stirrups in the ribs and floor beams. It was therefore appropriate expedient to verify the fitness for purpose and load-bearing reliability experimentally. Load tests in accordance with the guideline were ideal for this purpose.


Short list of references

Short list of references

Short list of references

  • Mosenschule school, Plauen, 2003
  • Old fire station, Plauen, 2004
  • Day nursery, Coswig, 2005
  • Residential building, Österreichviertel, Dessau, 2005
  • School for the deaf, Güstrow, 2006
  • Batschari Palais, Baden-Baden, 2007
  • Gut Gimritz, Halle (Saale), 2007
  • Leipzig University, historical balustrade construction, 2007
  • Factory production hall, St. Egidien, 2007
  • Nuremberg district court, 2008
  • B&B, Bad Aibling, 2008
  • Swimming pool building, Dresden, 2008
  • High school, Bad-Neustadt, 2008
  • Industrial building, Wernigerode, 2008
  • Leighton Barracks, Würzburg, Haus 131, 2009
  • King Albert Museum, Chemnitz, 2009
  • Neues Schloss primary school in Neustadt an der Donau Aisch, 2009
  • Leighton Barracks, Würzburg, Haus 129, 2009
  • Weinhold building, Chemnitz University of Technology, 2010
  • Schocken department store, Chemnitz, 2010
  • City library, Leipzig, 2010
  • Regional tax office, Chemnitz, 2010
  • Lindenfeld educational centre, Lutherstadt, Wittenberg, 2010
  • Harvey Barracks, Richthofen Circle, Kitzingen, 2010
  • Flaschenturm building, Berlin, 2011
  • Factory production hall with forklift traffic and fatigue analysis, Schweinfurt, 2011
  • Rotes Haus university hospital, Leipzig, 2011
  • 2nd factory production hall with forklift traffic and fatigue analysis, Schweinfurt, 2011
  • Bridge where the B180 crosses the A38 motorway near Querfurt, 2011
  • Secondary school, Regen, 2011
  • Mensa building, student union, Leipzig, 2011
  • 3rd factory production hall with forklift traffic and fatigue analysis, Schweinfurt, 2011
  • Historical balustrade construction, Halle, 2011
  • Roof construction of a factory building, Schweinfurt, 2011
  • Original balustrade on a former department store in Chemnitz, 2011
  • Former barracks building, Bad Aibling, 2012
  • Fall prevention from ventilation ducts in a factory building, Schweinfurt, 2012
  • Former barracks building, Friedrichshafen, 2012
  • Town hall, Dresden, 2012
  • Gallery loading, Merseburg, 2012
  • Roof loading with snow load monitoring, Plauen, 2012
  • Media centre, Mainz, 2013
  • Town hall, Dessau, 2013
  • Gustav Esche bridge, Leipzig, 2013
  • School, Bad Dürrenberg, 2013

 


Your point of contact

Working Group Leader
Dipl.-Ing. (FH)
Robert Herold
T +49 (0)341 6582-128
F +49 (0)341 6582-199