Shaking table test on a full scale URM cavity wall building

Abstract

A shaking table test on a two-storey full scale unreinforced masonry (URM) building was performed at the EUCENTRE laboratory within a comprehensive research programme on the seismic vulnerability of the existing Dutch URM structures. The building specimen was meant to represent the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. Cavity walls are usually composed of an inner loadbearing leaf and an outer leaf having aesthetic and weather-protection functions. In the tested specimen, the loadbearing masonry was composed of calcium silicate bricks, sustaining two reinforced concrete floors. A pitched timber roof was supported by two gable walls. The veneer was made of clay bricks connected to the inner masonry by means of metallic ties, as seen in common construction practice. An incremental dynamic test was carried out up to the near-collapse limit state of the specimen. The input motions were selected to be consistent with the characteristics of induced seismicity ground motions. The article describes the characteristics of the building and presents the results obtained during the material characterization and the shaking table tests, illustrating the response of the structure, the damage mechanism and its evolution during the experimental phases. All the processed data are freely available upon request (see http://www.eucentre.it/nam-project).

Appendices

Appendix 1

1.1 List of symbols

AMP _i :

Acceleration amplification (i = 1, 2, R for the 1st floor, 2nd floor and ridge beam levels, respectively)

a _R :

Acceleration at the ridge beam level

BSC :

Base shear coefficient (Eq. 3)

BSC _b :

Base shear coefficient of the bilinear approximation

E _m :

Elastic modulus of masonry

f _m :

Compressive strength of masonry

F _R :

Inertia force of the roof

F _Ry :

Yield load of the bilinear response of the roof

f _v0 :

Shear strength

g :

Gravitational acceleration

h _i :

Height of the ith storey

K _a :

Initial stiffness of the bilinear curve of the gable-roof system

K _b :

Secondary stiffness of the bilinear curve of the gable-roof system

K _Ri :

Effective stiffness of the gable-roof system (i = test identification number)

L _R :

Inclined length of the roof pitch

M :

Total mass of specimen

mHI :

Modified Housner intensity (Eq. 1)

PSV :

Pseudo spectral velocity

V :

Base shear

Sa :

5% elastic spectral acceleration

T _1,i :

Fundamental period (i = test identification number)

γ _R :

Shear deformation of roof diaphragm (with the residual shear deformations)

γ _R,res :

Residual shear deformations of the roof diaphragm

$\tilde{\gamma }_{R}$ :

Shear deformation of roof diaphragm (without the residual shear deformations)

Δ _i :

Displacement (i = 1, 2, R for the 1st floor, 2nd floor and ridge beam levels, respectively)

Δ _Rmax :

Maximum displacement of the roof

δ _R :

Relative displacement of the ridge with respect to the second floor level

δ _Ry :

Yield displacement of the roof bilinear response

δ _Ru :

Ultimate displacement of the roof bilinear response

θ _i :

Peak inter-storey drift ratio (i = 1, 2 for the 1st floor and 2nd floor, respectively)

θ _i,res :

Residual inter-storey drift ratio (i = 1, 2 for the 1st floor and 2nd floor, respectively)

$\tilde{\theta }$ :

Global drift (Eq. 2)

$\tilde{\theta }_{DSi}$ :

Global drift threshold (i = damage state)

$\tilde{\theta }_{y,b}$ :

Yield global drift of the bilinear approximation

$\tilde{\theta }_{u,b}$ :

Ultimate global drift of the bilinear approximation

μ :

Friction coefficient

Appendix 2

The present section provides guidelines for the use of the lab data obtained by the acquisition systems that can be found in the following location: http://www.eucentre.it/nam-project/. Photos and videos from all the testing phases can be requested at the same URL.

2.1 Traditional acquisition system

The data are available in files with .txt format, organised in matrix form, where the information recorded by each instrument is listed in columns. Each.txt file is named after the corresponding shake-table test, in accordance to Table 3. With reference to Fig. 9, Table 5 lists the type of information given in each data column, as well as the associated instrument location. Some of the accelerometers are accompanied by the portion of the structural mass that was considered in computing the inertial forces. The first column represents the data acquisition time step, while columns 2–53 contain the acceleration time-histories recorded by the accelerometers mounted on the structure. All the data recorded directly by instruments (2–83) are raw data filtered by means of a quadratic low-pass filter set to a frequency equal to 50 Hz. The displacement histories recorded by wire potentiometers are listed in columns 54–63, while those recorded by traditional potentiometers are found in columns 64–80. Columns 81, 82 and 83 contain the actuator read-out data, in terms of horizontal (x direction) forces, displacements and accelerations. The last columns (84–93) contain quantities that were not directly measured but computed, such as the total base-shear force and the inter-storey drift ratio time-histories (Table 5).

Table 5 Content of the data matrices

2.2 3D optical acquisition system

The data obtained by the 3D optical acquisition system (Fig. 21) can be found in the same database. The synchronized data are provided for the shaking-table tests listed in Table 6, organized in.C3D files.

Fig. 21

3D optical acquisition system (markers illustrated with white dots)

Table 6 Summary the data obtained by the 3D optical acquisition system

The.C3D files can be opened in MATLAB using the.m file provided with the data (an example is also available “Post_Process_EUCENTRE_Example.m”).

The label and position of each marker is illustrated in Figs. 22 and 23. In some cases, the trajectories of some markers was not reliably recorded, as a consequence the corresponding data have been removed from the data matrices. In particular, the missing marker are listed in Table 7.

Fig. 22

3D optical acquisition system: markers mounted on the North façade of the building specimen

Fig. 23

3D optical acquisition system: markers mounted on the West façade of the building specimen

Table 7 Markers missing from the final provided data matrices

The coordinates of the markers are given in mm. Although the absolute residual displacements can be extracted from the data collected during each individual test, the measurements do not include reliable residual displacements resulting from previous tests. This happens due to the slight change of the reference system adopted after the calibration of the 3D optical system performed in the beginning of every test (problem solved in tests conducted after this one). For example, in order to compute the residual displacement of a given marker through various tests, the suggestion is to use relative position (e.g. consider marker A011 as origin of x axis) and sum all the residuals recorded at the end of each test or directly refer to traditional instrumentation data. The relative position of markers (useful for the computation of deformation and the residual deformation) within each test is not affected.