The influence of Hennebique and his licensees in the German Empire was rather indirect (7), for example in Berlin only eight buildings were realized between 1899 and 1901 by Hennebique i.e. his licensees (8). Nevertheless his ideas (see figure 2) affected the development of reinforced concrete. The more than vivid discussions between scientists and engineers in the German Empire and other European countries, on the characteristics of reinforced concrete are documented in an extensive number of articles and books. These efforts eventually led to the 1st regulations for building with reinforced concrete in Prussia (9). These had various impacts on building in Berlin. Firstly it offered a more unified calculation routine that could be applied. Secondly it specified the positioning of reinforcement especially for columns and beams. Thirdly because of a more reliable assignment of building permits more companies became part of the reinforced concrete building market besides the famous Beton- und Monierbau A.G., originally founded by G.A. Wayss. For example names such as Baugesellschaft für Lolat-Eisenbeton GmbH, Keppich Eisenbeton or Eisenbetonbau Konrad Schwartz GmbH are now documented.

Leaving aside the different ceiling systems that were available (10), early reinforced concrete in Berlin generally features its own characteristics. Documented findings show ceiling structures with small diameter reinforcement mesh (6-10 mm) and beams and columns with larger reinfocement bars (16-23 mm) and stirrups with (6-8mm).

It is specific in the history of reinforced concrete, that frames give a good example of how “[i]n the historical process, the structural engineer [only] gradually discovers the internal logic of the structures he has invented […]” (11, p. 528). In the beginning reinforced concrete in buildings was not understood as a complex loadbearing structure, rather single elements such as beams and columns were calculated without composite effects. Nevertheless the way of construction in itself produced somewhat monolithic joints. In 1907 the first publications appeared discussing ways to calculate rigid frames (11, p.529), followed by a book (12) published in 1909 that included structurally indeterminate frames. Despite the increasing theoretical knowledge, examples in Berlin show that it took some time before the theory was put into practice.

The warehouse design combines a silo and a floor storage unit, featuring a reinforced concrete loadbearing structure that is partly visible from the outside. The building is 20 (m) wide and 60 (m) long, with an eaves height of about 20 (m) (see figures 3, 4 and 5). It is divided into six floors as well as a basement.

The internal layout of the floor storage features three rows of internal columns with a distance of 4.84 (m) in between. The distance from the outermost column to the outside walls is 5.03 (m). In longitudinal direction the distance between the internal columns is 4.44 (m) and to the gable 4.64 (m).

In between columns spans a system of vouted primary (60 (cm) height) and secondary (35 (cm) height) beams. The cross section of columns varies on each floor, from 65 by 75 (cm) in the basement to only 35 by 35 (cm) in the attic.

The structural calculation from 1909/10 is documented in the building archive. In general it can be characterized with a very clear, almost standardized structure, following the flow of loads from top to bottom. The calculations in typewriting are supplemented by small pronouncing illustrations. In addition to manual sketches of special load positions, illustrations can also be found for reinforcement distribution and concrete cover for which apparently standardized stamps were used (see figure 6). These suggest that the company routinely carried out structural calculations for reinforced concrete.

The basis of the calculation was the 1907 regulation published by the Prussian building authorities (14). Accordingly, the beams were calculated as continuous. The length of the columns corresponds to the height of each floor.

Based on the documented archive material snow and wind loads were only applied within the calculation of the roof structure. Taking into account the silo storage part of the building the actual stiffness appears sufficient, but nevertheless there was no proof at all for overall wind loads. For live loads 1000 (kg/cm²) were applied.

For a more detailed analysis of the calculation and the design of the reinforcement a focus is put on the floor storage part of the building. Here the ceiling slabs and beams were calculated as continuous, with negative moments above supports. For shear stress a maximum of 4.5 (kg/cm²) was taken into account. In areas with higher shear stress, reinforcement using stirrups was specified, though no details of the form of these stirrups were given.

A maximum of 40 (kg/cm²) for the compression strength of the concrete was decisive for dimensioning the columns cross section. Irrespective of their size all columns are reinforced with four longitudinal bars, one in each corner. Horizontal stirrups were not calculated.

With the building still existing today, it was possible to investigate parts of the floor storage on the 3rd floor using non-destructive measuring devices such as a Profometer 5+. Due to the restricted access the results are somewhat limited. Nevertheless it was possible to compare them with archive material (see figure 7).

In conclusion it can be said, that the reinforcement generally meets the specifications in the structural calculation of that time. The ceiling slabs for example show a cross wise reinforcement using diameters of less than 20 (mm) with a spacing of 6 (cm) for the main and 15 (cm) for the transverse reinforcement. Beams are reinforced using also diameters smaller than 20 (mm) and positioned in two layers. The secondary and primary beams were reinforced with stirrups showing a general spacing of 20 (cm) in the field and 10 (cm) close to supports. For columns one reinforcement bar in each corner and also horizontal stirrups with a spacing of 40 to 65 (cm) were detected.

The building (see figure 8) can be divided into three parts: the living quarters (not visible), the entrance (left) and the hall part (right). Only the hall part of the building features a storey frame. The two-hinged story frames surround the middle hall on three sides (see figure 9 and 10). The frames have a span of 7.10 (m) and a varying height of 2.7 (m) in the basement and 5.0 (m) on the ground floor. The beams have a cross section of 30 by 50 (cm) and vouted endings connecting to the columns. The cross section of the columns is continuously 80 by 80 (cm). In between the frames ceiling slabs span the distance of 2.7 (m).

Originally, the design featured a set up similar to the Victoria warehouse. The structure was composed of ceiling slabs and beams in combination with single storey columns. When analyzing the structural calculations it becomes apparent that due to the input from a specialized contractor the idea of monolithic reinforced concrete frames became part of the design.

Only then bending moments were taken into account where the beams connect to the columns. Thus, parts of the building became one of the first truly calculated monolithic reinforced concrete frames in Berlin (see figure 11). Although the contractor providing the calculation was a specialized company the realization of the structure shows some remarkable deficiencies that will be described in the following paragraph.

An investigation after World War 2, in 1953 showed remarkable discrepancies between the planned and the realized reinforcement (15). As part of the PhD research an additional investigation was carried out in parts of the basement and ground floor. While the reinforcement of the ceiling slabs seems correct, the beams show less reinforcement than planned. About 40% of the longitudinal reinforcement was left out. The stirrups appear to have a diameter of about 7 (mm) and a spacing of 30 (cm), while originally flat iron bars were designed. The reinforcement of the columns shows a longitudinal bar in each corner and therefore meets the requirements. The horizontal stirrups within the columns appear to have a smaller diameter of 7 (mm) and spacing of 35 (cm) compared to a 10 (mm) diameter and a spacing of 60 (cm) as originally planned. Furthermore, the form of the stirrups seems to be somewhat irregular and does not follow the outer geometry of the column.