Higher frequency dynamic response analysis of the foam concrete block element

In civil engineering structures frequency response are often low. There are some special tasks in innovative material parameters investigation where higher frequency response is important. The small dimension samples are often used to determinate material properties. This paper contains analysis of the natural modes and natural frequencies the foam concrete block sample.


Introduction
A new progressive modern materials are using in civil engineering more and more.One of this material is unconditionally the foam concrete.Many engineers and researchers are interesting in study of this material all over the world.The basic static and dynamic parameters are important to determinate for each mixture of basic foam concrete components.This paper shows how it is possible to determinate the basic dynamic parameters of simple shaped sample made from the foam concrete.

Experimental object description
The foam concrete block is really simple modelled type of sample.It has some special material properties and it has to be investigated.Small dimensional experiment on sample is effective to study higher frequency response of the dynamic behaviour.For this purpose, the experimental sample was casted into the mold with nominal dimension 10x10x40 cm (Figure 1).After several hours the overflowing part cuts off.The surface of wet concrete block is covered with foil.After 3 days the tested block freed from the mold and it is packed to the foil.All tests can be applied after 28 days from this process.The unit weight of the real investigated sample is measured and identified as 582 kg/m 3 .Modulus of elasticity are E stat = 521 MPa and E dyn = 611 Mpa.These parameters were obtained from standard material tests for material type FC500 -IWTECH.More detailed research about the foam concrete material and technical parameters is in [1,2,3].The investigated sample is stiff fixed in first 10cm on upper and down area to hard leaden block.

Numerical and experimental results
Numerical model was created in VisualFEA system based on Finite Element Method (FEM).VisualFEA is integrated system for finite element analysis, which is an advanced numerical technique to solve and analyse physical problems arising in many fields of science and engineering. [6]FEM model of the sample respect all geometric, material and

Fig. 1 .
Fig. 1.The foam concrete with installed measurement equipment

Fig. 3 .
Fig. 3. ARTeMIS software processing example.ARTeMIS Modal includes up to three frequency domain modal analysis techniques derived from the patented Frequency Domain Decomposition technology utilizing the singular value decomposition of the estimated spectral densities of the measured response.The techniques available are: • Frequency Domain Decompostion -FDD.• Enhanced Frequency Domain Decompostion -EFDD.•Curve-fit Frequency Domain Decompostion -CFDD.[5]

MATEC 3 .Fig. 4 .Fig. 5 .
Fig. 4. Natural frequencies and natural modes FEM model obtainedFor the experimental modal analysis was investigated upper area of the foam concrete block.The uniform grid 5x6cm with 12 Deltatron accelerometers type 4508 B 002 were installed on this area (Figure1).Accelerometers were connected to two Input Module Type 3050-B-060 and the other PULSE compatible software and hardware accessories specified in chapter 2. The excitation was performed with a soft tapping all over the sample surface.Measured data were transformed to ARTeMIS system and processed using FDD.The relevant frequency broadband of the dynamic response is 100 -900 Hz and resulted modes of natural vibration of the frame are presented in Figure5.There is also MAC (Modal Assurance Criterion) values are also presented in bar graph on Figure2which indicates validation of the modal parameters.