🕑 Reading time: 1 minuteThere are various types of loads such as ground borne vibration, vibrating machinery, human induced excitation, etc. that cause vibration serviceability problems in building structures. These loads will be discussed in the following sections.
Fig.1: Floor vibration simulation and test
What is the Vibration Serviceability for Building Structures?When a structure demonstrates vibration behavior that create uncomfortable environment and disturb occupants and hinder a proper operation of sensitive equipment, then the structure is said to fail in terms of serviceability requirements. By and large, the stresses and strains generated due to such vibration are substantially small and considerably smaller than the value for which the structure is designed for. Therefore, the structure would not experience ultimate limit state collapse. Nonetheless, it would not be suitable to serve the goal for which the structure is designed and constructed. Examples of structures that may suffer from serviceability issues include slender floors which may be used in hospitals, residential buildings, offices, and other Buildings. Another example of structures that is likely to encounter serviceability issues is sport stadia. This structure is commonly support thousands of people. Finally, slender staircase and footbridges are also susceptible to vibrations problems.
Types of Loads Causing Vibration Serviceability Problems in Buildings
Ground Borne VibrationOne of the three major types of loads that lead to serviceability issues in structures is the ground borne vibration. Ground bore vibrations are possibly transmitted through ground from vibration sources such as heavy construction activities, railways, and roads to the structure. The transmitted vibrations could be enough to halt sensitive equipment operations and make occupants uncomfortable. It is considerably unlikely that ground borne vibrations cause structural damages. This type of serviceability problem cannot be tackled easily, and most of solutions are focused on source of the problem. For example, breaking vibration transmittance path by digging a trench and filling the trench using suitable material for instance gravel. The density of the material used to fill the trench should be different from ground soil density. Figure 3 and Figure 4 shows the source of ground borne vibration and its transmission to the structure.
Fig.3: Ground borne vibration in buildings
Fig.4: Ground borne vibration in buildings
Vibrating MachineriesThis type of vibration load is imposed on structures by machines and equipment placed inside the structure, for example, photocopier, mechanical and electrical plant, and left motors. Such machines may create serious period dynamic excitation that leads to severe serviceability issues. These problems can be tackled by placing machines and equipment on anti vibration mountings. As a result, vibrations produced by machines would not reach the structure.
Fig.5: Anti-vibration mountings
Human Induced ExcitationCommonly, human activities are the source of human induced excitation. It may occur frequently over a period of time for instance in the case of walking or impulsive and isolated such as jumping. Unlike other two types of vibration load sources, human induced excitation cannot be separated from the structure and they generate considerable vibrations in the structures which they are settled in. Therefore, it is required to design and construct the structure to cope with human induced excitation and consequently avoid vibration serviceability problems. Due to the same reason, the majority of guidelines and specifications in world have focused on human induced excitation. The most problematic types of human induced excitation are periodic ones since one or more of this human dynamic excitation could lead to resonance which is astronomically undesirable and cause substantial problem in a structure. Loading of periodic human dynamic excitation is described by Fourier series equation which can be found below. Where: G: is the weight of a single individual TP: is the activity repetition period (1/TP is the activity frequency) rn and : are taken from table 1 There are various Fourier series coefficient that established by researchers using measured forces generated by different human activities. These coefficients of Fourier series for various human activities including jumping can be found in Table 1. Fourier series equation can be used to compute forced of single person and group of individuals.
Table-1: Fourier series coefficients for various activities including jumping
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