Influence of vibrations on structures

Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 293 Influence of vibrations on structures Zdeněk Kaláb1 One type of occasional structural load is a seismic load. Earthquakes and blasts are typical sources of vibrations, but vibration generated during urban tunnel construction can represent a significant problem. Evaluation of the harmful impact of vibrations transmitted through rock massif into buildings is solved using experimental measurements, detailed analyses of measured signals, knowledge of geological pattern and constructional analysis. Seismic load of structures due to earthquakes is solved using the EUROCODE 8 standard. The earthquake movements at a certain location on the surface are determined by an elastic response spectrum to the ground acceleration. Eurocode 8 puts emphasis especially on the robust foundations and simplicity of construction systems. It is also mentioned vibration effect on historical buildings and effect under the surface, for example, in mine spaces. Historical structures are usually even more prone to vibration damage than, for example, typical wood-frame homes. The greater concerns over historic structures arise from the design, structure age, building materials and building methods used. The peak values of vibration generated by earthquake decrease with depth; the decrease is faster in shallow layers compared with the deeper part. Technical vibrations differ from natural earthquakes, for a comparable value of maximum vibration amplitudes, especially in the frequency range of the signal and mostly its duration. Evaluation of technical seismicity is more complicated because there are usually used national standards. To document some common information about vibration effects on structures, some experimental measurements are presented. Examples of real wave patterns document common shapes and also signals with significant resonant vibrations. Very interesting is an example of resonant vibration that was generated as the influence of basin structures on the shape of wave patterns due to quarry blasts. To obtain complete information, measurement system has to keep sufficient parameters, especially the frequency range of the whole seismic channel, sampling frequency, and proper anchoring of the sensor. The basic methodology for evaluation of vibration on structures is outlined. Keywords: seismic load, seismic standard, Eurocode 8, earthquake, technical seismicity Introduction The basic objective of all activities in the designing and realisation of structures must be to create a quality environment suitable for the intended purpose of the structure, while this quality should be maintained over the entire expected life of the structure. The basic requirements for structure construction are (according to Merritt and Ricketts, 2001; Macdonald, 2001; Chudley and Greeno, 2014):  Architectural requirements;  Structural static requirements;  Resistance to external influences;  Welfare and hygiene requirements for the indoor environment;  Operational safety requirements;  Technology requirements;  Economic requirements;  Environmental requirements. A load of structures can be classified as follows:  Occasional loads (long-term, short-term, extraordinary) o Payloads; o Climate loads; o Snow load; o Wind load; o Frost load; o Load from forced strains; o Temperature load; o Load by rheological material changes; o Load by deteriorating support; o Mounting load; o Seismic load; o Pressure waves; 1 Zdeněk Kaláb, VŠB – Technical University of Ostrava, Faculty of Civil Engineering, L. Podéště 1875, 708 00 Ostrava – Poruba, Czech Republic, [email protected] , Institute of Geonics of the CAS, Ostrava – Poruba, Czech Republic Zdeněk Kaláb: Influence of vibrations on structures 294 o Emergency load.  Permanent loads o Load by the weight of the structure; o Pressure load; o Preloading. In order to assess the seismic load (vibrations) of structures, we need to determine the safe boundary that does not break the object or release the rock. The occurrence of new cracks or the widening of existing cracks, in the case of structures such as a drop of mortar or plaster or falling-off rock fragments, is considered a failure in both cases mentioned above (for example, Tripathy et al., 2016; Zeigler, 2018). It is necessary to prevent catastrophic failure, i.e., collapsing the structure (Fig. 1) or rocking off, at all times (for example, Towhata, 2008; Villaverde, 2009). On the other hand, cosmetic (light) damage is allowed in some cases if it does not compromise the safety of the structure. To do this, it is necessary to know the appropriate criterion for assessing the vibration effects that can be measured and potentially extrapolated on the endangered structure. Further, the degree of violation must be distinguished more precisely, and finally, we should have the possibility of a preliminary estimate of the vibration effects. The assessment of seismic load of structures often results from the measurement of vibrations at the reference standing place (for example, standard ISO 4866). In order to assess the response of structures, records should be obtained for such intensity of vibrations that evoke measurable effects on the structures. Vibration records have to be realised in an adequate time and frequency ranges (for example, Scherbaum, 1994). Fig. 1. A man walks past a collapsed building in Dabandikhan in Sulaimaniya Governorate, Iraq. (Photo by Ako Rasheed, Reuters; Received from http://www.interaksyon.com/toll-from-iran-iraq-quake-breaches-450/ ). As an example, typical damages in a masonry building are presented in Fig. 2 (according to www.earthauroville.com/index.php). Structural elements, such as walls, columns, and beams, are only bearing the weight of the building and the live load under normal conditions: mostly compression forces for the walls and columns, and vertical bending for the beams. Under dynamic load, they also have to withstand horizontal bending and shear forces, and extra vertical compression forces. Several types of cracks are possible to define (Fig. 2). It is necessary to point out that small amounts of cosmetic cracking can arise from slight settling, ground movement, temperature, and humidity cycling, and even, in extreme cases (hurricanes, tornadoes), wind loading (Zeigler, 2018). Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 295 Fig. 2. Typical damages in a masonry building (according to www.earth-auroville.com/index.php) 1: Diagonal shear crack of piers, 2: Horizontal shear crack of long pier, 3: Bending cracks at feet and lintels, 4: Bending crack of wall (bad corner bond), 5: Bending crack of spandrel, 6: Bending crack of gable, 7: Plaster peeling off, 8: Crushing of weak masonry under vertical ground motion, 9: Damage of corner eaves under vertical ground motion, 10: Badly anchored roof, pulled out by vertical ground motion, 11: Falling of tiles from the roof eave, 12: Damage of tiles roof with shear (roof not braced). To properly support a structure in response to whatever loads may be applied to it, a structure must possess four properties: it must be capable of achieving a state of equilibrium, it must be stable, it must have adequate strength, and it must have adequate rigidity (Macdonald, 2001). The achievement of stable equilibrium has been shown to be dependent largely on the geometric configuration of the structure and is, therefore, a consideration which affects the determination of its form. A stable form can almost always be made adequately strong and rigid, but the form chosen does affect the efficiency with which this can be accomplished. Therefore, collaboration has always been required between architects and those who have the technical expertise to realise building construction (for example, Merritt and Ricketts, 2001; Chudley and Greeno, 2014). Every structure has vibration frequencies and mode shapes that are called "natural frequencies“ that can be found by using analytical methods. Calculation of these frequencies and their mode shapes are important to solve the vibration induced engineering problems. However, complex shaped objects can only be analysed by numerical methods. In particular, finite element methods (FEM) and boundary element method (BEM) enable to investigate the natural frequencies and mode shapes of complex structures by idealising them into computable small parts (for example, Berr, 2003; Hori, 2006; Chakraverty et al., 2012). Vibration analyses can be divided into two main parts. These are natural frequency and mode shape extraction and forced vibration analysis. By natural frequency analysis, the object's natural frequencies are obtained. A frequency of a periodic force which is applied to this object could be near to one of the object's natural frequencies. If so, that frequency is excited, and the structure starts to vibrate in its mode shape and natural frequency. If excitation frequency comes across the structure's natural frequency, "resonance" event occurs. In many case resonance is undesirable, and either excitation frequency or structure's natural frequency should be changed (http://www.mesh.com.tr/vibrationanalyses.html). The examples of analysis of the impact of vibrations on structures are presented in this paper, which is based mainly on the Eurocode 8 standard. Although this standard deals with the design of earthquake resistant structures, general rules apply to technical vibrations too. It is also necessary to point out the most common fundamental differences between natural and technical vibrations (at comparable amplitude values), which is especially the frequency range of the signal and mostly its duration. International standard ISO 4866 introduces Zdeněk Kaláb: Influence of vibrations on structures 296 frequency range 0.1 – 30 Hz and velocity amplitude range 0.2 – 400 m.s-1 for earthquakes. For quarry blasts, it introduces frequency range 1 – 300 Hz and velocity amplitude range 0.2 – 500 m.s-1, and for other technical sources frequency range usually 1 – 100 Hz (up 1 kHz for machines) and velocity amplitude range up 0.2 – 50 m.s-1. Several examples of vibration records realised in a different type of structures, as mentioned at the end of this paper, document variability of structure responses. Vibration movement Theory of vibration movement, especially harmonic vibration, is commonly known and it is described in many textbooks, including seismological literature (for example, Bullen and Bolt, 1985; Kulhánek, 1990; Doyle, 1995; Udías, 1999; Shearer, 2009). The ground motions that are produced by earthquakes can be completely described by six components of motion, i.e., three translational components and three rotational ones, and by deformation (for example, Båth, 1979; Teisseyre et al., 2006; Graizer, 2006). Usually, only translational components are used for interpretation. Rotational components have been known for several centuries. However, it is only during the last two decades that greater attention has been dedicated to precise measurements of these. Although rotational components usually have small values, several studies have shown the importance of these components in seismological analyses and engineering applications (for example, Lee et al., 2009; Knejzlík et al., 2012; Kaláb et al., 2013). Seismic movement can be described by the time variations of the ground acceleration and its associated parameters (velocity, displacement). The maximum (peak) ground acceleration, duration, and frequency content of earthquake can be obtained from an accelerogram. The seismic movement must be composed of three simultaneously acting accelerograms (calculated, actual, and simulated) in the case when a spatial model is to be considered. If particular constructions are evaluated, it is possible to describe the ground movement as a function of location and time. The damage potential of a given vibration is often assumed, even by those who do vibration monitoring, to be governed only by the maximum ground velocity of the vibration. However, the detailed frequency component makeup of the vibration, its duration and the number of times it is repeated all contribute to its potential for causing damage (for example, Lyubushin, 2007; Lyubushin et al., 2012; Zeigler, 2018). We distinguish primary and secondary members as regards vibration of structures. A certain number of supporting elements can be designed as secondary seismic members, which do not form part of a seismic loadbearing structure. These are all parts of structures that hold something up but are not crucial to the building’s structural integrity. The strength and stiffness of these members against seismic actions shall be neglected. These members and their connections shall be designed and constructed to maintain support of gravity load when subjected to the displacement generated by the most unfavourable seismic design condition. All structural elements that are not designed as secondary are considered as primary seismic members (see Eurocode 8). It means everything without which the structure will not stand up (typically columns, braces, and beams in steel constructions, add shear walls and slabs in concrete constructions). It is considered to be part of the load-bearing system that is resistant to transverse forces (for example, Iervolino et al., 2008). As mentioned above, vibration load can be expressed in several ways. The earthquake movement (i.e., natural origin) at a certain location on the surface is determined by an elastic response spectrum to the ground acceleration (for example, Gupta, 1992; Viskup et al., 2005). The shape of the response spectrum is assumed to be the same for both seismic loads levels (i.e., the ultimate limit state and damage limitation state). The horizontal load is described by two independent perpendicular components (but with identical spectra). One or more different response spectra are used for all three components (occasionally a vertical component is also used) of the seismic load depend on the source parameters and magnitude of the earthquake. Also, more than one spectrum should be considered if earthquakes threatening the evaluated locality can come from directionally different source areas (for example, Bolt, 1999; Udías, 1999). In the last mentioned situation, different values of design acceleration values ag will have to be defined for each spectrum type and earthquake. Response spectra (Fig. 3) are used to provide the most descriptive representation of the influence of a given earthquake on a structure (for example, Ali et al., 2017). The guiding principles governing this conceptual design are (Eurocode 8):  Structural simplicity;  Uniformity, symmetry, and redundancy;  Bi-directional resistance and stiffness;  Torsional resistance and stiffness;  Diaphragmatic behaviour at storey level;  Adequate foundation. Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 297 Fig. 3. Spectral shapes for main site classes (labelled as A – E). (Received from Iervolino et al., 2008). In design calculations, structures are to be modelled, designed and modified according to the Eurocode rules. In terms of seismic design, the structures are categorised into regular and non-regular (which have an impact on the design model, the calculation method and the coefficient of ductility). The criteria for regularity in plan and elevation are defined. Buildings are classified in 4 importance classes, depending on the consequences of a collapse for human lives, on the importance for public safety and civil protection in the immediate post-earthquake period, and the social and economic consequences of collapse (Eurocode 8). In the Czech Republic (National annex of the Eurocode 8), the following values of the importance factor γ are used: I = 0.8; II = 1.0; III = 1.2; IV = 1.4. The Eurocode 8 puts emphasis especially on the robust foundation and simplicity of construction systems. This standard also allows differentiation of constructions according to their importance, their dimensions, and their mechanical action. Among other things, the standard specifies conditions for building site selection, soil parameters and also criteria that ground and foundation systems have to complete in seismic design situations. Eurocode 8 provides a simple quasi-static solution for ordinary buildings; seismic forces that already include the effect of motion are determined. Generally, horizontal excitation is used because vertical excitation is usually smaller, and structures are even more resistant to this direction because the design of structures respects their weight. Vertical loads can be of use both in the areas near the epicentres and in the case of long brackets or beams loaded with non-pillar columns. It is also necessary to take into account that loads of buildings and structures by technical seismicity and their responses are evaluated according to, for example, Czech Technical Standard 73 0040 or Slovak Technical Standard STN EN 1998-1/NA/Z1. This evaluation is established using a class of resistance (A – F) and class of economic and social significance of buildings (U, I – III). Structures of A type are usually historical monuments and buildings, the oldest and poorly structures and also buildings with large plastic decoration; structures of B type are common masonry buildings, usually up to three levels and surface up to 200 m2. Determination of resistance class depends also on the constructional technology and material used. From the constructional point of view, there are monolithic structures with resistance class E, framed structures with class D, half-timbered structures with class D, buildings up to three stories with class B and prefabricated panel structures with class C. Resistance class can be determined based on material used: stone - resistance class A, masonry - resistance class A, B, C, concrete - resistance class C, D, steel - resistance class D, E and steel concrete – E. Class of significance U represents structures with extraordinary economic and/or social significance (for example, dams, significant bridges …), following class I is represented by structures with great significance (for example, schools, churches…), classes II and III include structures with medium and small significances, respectively. Zdeněk Kaláb: Influence of vibrations on structures 298 Historic structures (class A) are usually even more prone to vibration damage than typical wood-frame homes. The greater concerns over historic structures arise from the design, structure age, building materials and building methods used. Maintenance can be an issue in some cases, as well (Johnson and Hannen, 2015; Bongiovanni et al., 2017). For example, tower structures were often built by Romans to celebrate military victories. They played an important role in the reconstruction of some historical periods, but also in the study of the historical seismicity (for example, Bongiovanni et al., 2014). And further example, Clemente et al. (2002) analysed the experimental seismic behaviour of a bell tower damaged by the 1996 Reggio Emilia earthquake. Naturally, engineered, steel-reinforced buildings are more resistant to vibration damage than engineered, nonreinforced structures. All authors, not only describing historical structures loading, pointed out the importance of a multidisciplinarity approach to analyse and preserve given structure. A most important article on amplitude versus depth relationship was published by Chinese researchers Hu and Xie in 2004. The following information was extracted from this article. The ratio of the amplitudes in the observed depth (underground) and the surface is used for the examination of changes in the value of vibration relative to depth (underground amplitude/surface amplitude). The amplitude ratio is calculated from the maximum values, which can be measured as the peak ground acceleration (PGA), the peak ground velocity (PGV) or the peak ground displacement (PGD). The reason for choosing the surface value as a comparative value is the following. In general, the value of the maximum surface amplitude is greater than in the underground, so if we use a larger value in the denominator, the relative error is reduced. Further, the surface records are much more frequent than from underground; therefore the values for the underground can be determined using statistical regression curves. The evaluation procedure is as follows: Firstly, we issue from the data recorded by a network of seismic stations; to study the effects of earthquakes depending on the depth, the recorded data are split into groups depending on the magnitude of the earthquake and peak amplitude. Secondly, it is possible to calculate the value of amplitude ratios for earthquakes of the same group. Based on this, the average size ratio of all the earthquakes of the same depth can be determined, thus obtaining the average amplitude ratios at different depths. Thirdly, the curves of average amplitudes for each group of earthquakes are determined using non-linear regression analysis. For research purposes, the value of the horizontal component amplitude is determined as the average of two components (NS and EW in the geographic positioning of seismometers). The Dowding´s and Rozen´s study (1978 in Varnusfaderani et al., 2015) divides the damage to underground structures into three categories according to the effects of the earthquake: damage caused by vibrations, damage caused by faults and damage caused by disturbances due to the earthquake, for example, soil liquefaction or landslides. Varnusfaderani et al. (2015) also pay attention to the source mechanism of earthquakes. Manifestations of underground seismic activity can be divided into two categories:  Vibration - changes in stress-strain conditions;  Loss of stability - soil liquefaction, a fault in the rock massif, landslides. Three types of deformation caused by seismic vibration appear in linear structures located in the underground (Owen and Scholl, 1981):  Longitudinal axial deformation caused by pressure or tension;  Bending of the direction axis of a tunnel;  Deformation of the circular section into oval or frame deformation (racking). Although the variation characteristics of PGA in different sites share some common features, as shown in Fig. 4, there are still some differences which can be summarised as follows. What is needed to say is that although the events are not quite enough in soil/rock site to account for the specific reduction characteristics of PGA, in order to illustrate the essential characteristics between different site conditions we still compared the two sites.  The PGA decline velocity for soil/rock site is the most rapidly, for rock site it is the least rapidly, and for soil site, it is in the middle of the two sites.  The variation of PGA with depth is affected by the magnitude of earthquakes and site geology. For soil site, the PGA decreases with the increasing of magnitude or intensity; for rock site, the declining extent of the larger earthquakes is more rapidly than that of the smaller's.  Different from rock site, for soil site, there is a dramatic declination in the shallower layer. Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 299 Fig. 4. The comparison of PGA ratios in different sites (from Hu and Xie, 2004). Based on the results of Hu and Xie (2004), it drew some general conclusions:  In general, the earthquake amplitude (PGA, PGV or PGD) decreases with depth, and the declining extent is more dramatic in shallower layers than that in deeper ones.  The reduction of amplitude with depth is affected by the magnitude and site geology. In general, for soil site, the declining extent decreases with the increment of magnitude as well as the amplitude.  For soil site, as shown in Fig. 5, the decline velocities of PGA, PGV and PGD decrease in sequence. For soil/rock site, the decline velocities of PGA, PGV, and PGD are similar to each other. Fig. 5. The comparison of PGA, PGV and PGD ratios in soil sites (a) and soil/rock sites (b) (from Hu and Xie, 2004). Results imply that PGA decreases with depth and the decline mainly focus on shallower layers. For example, the PGA in depth of 25 m decreases to 1/2 that of the surface. Moreover, as we all known in seismic response analysis, the input motion for structures are generally deduced from the design intensity of surface, and then the surface motion, like PGA, PGV, PGD or time histories, are put to the bottom of the buildings. Obviously, it is inappropriate for that the depth of burial of underground structure or high-rise buildings are always more than 10 m, and the general ideas of doing so are that it would lead to an overestimate of seismic response. Zdeněk Kaláb: Influence of vibrations on structures 300 The issue of manifestations of earthquakes in underground mines is in the interest of responsible workers for many years. As an example, we present the findings which were published in a comprehensive study already in 1978 by Pratt, Hustrulid and Stephenson of Utah. Stevens (1977 in Pratt et al., 1978) summarises the nature of earthquakes and lists numerous examples concerning the earthquakes manifestations on underground structures. He has several general conclusions:  Effects on mines are less severe than surface effects. o Severe damage is inevitable when a mine or tunnel intersects a fault along which movement occurs during an earthquake; o Mines in the epicentre region of strong earthquakes but not crosscut by fault movement may suffer severe damage by shaking. Stevens did not define the word severe quantitatively; o Mines outside of epicentre regions are likely to suffer little or no damage from a strong earthquake;  Damage to mines is most insignificant when they are located in highly competent, unweathered rock; greatest damage occurs in mines found in loose unconsolidated or incompetent rock. This is due to the diminished effect of shaking in competent rock; unconsolidated sediment is much more susceptible to damage caused by vibration. Principal conclusions developed in this study are:  There are very few data on damage in the subsurface due to earthquakes. This fact itself attests to the lessened effect of earthquakes in the subsurface because mines exist in areas where strong earthquakes have done extensive surface damage.  More damage is reported in shallow tunnels near the surface than in deep mines.  In mines and tunnels, large displacements occur primarily along pre-existing faults and fractures or at the surface entrance to these facilities.  Data indicate vertical structures such as wells and shafts are less susceptible to damage than surface facilities. Parametric studies were carried out to investigate the influence of the desired variables on the dynamic behaviour of an underground structure while earthquake loading (Serati and Moosavi, 2010). To perform a sensibility analysis of a particular parameter, a suitable model based on all important concepts of dynamic analysis was created. Then by changing the desired parameter in the selected range and keeping all other conditions of the model (such as model dimension, element size, etc.) constant, acceleration, displacement and velocity histories around the underground structure were calculated. Finally, the spectrum was obtained so that its independent variable was the desired parameter and its dependent variable was the maximum amplitude of velocity, displacement or acceleration history. Examining the obtained spectrum shows how changing in the desired parameter can affect dynamic records amplitude around the basic model of the underground structure. The greatest impact on the dynamic behaviour of the underground of structures during an earthquake in terms of geotechnical parameters is seen on the elastic modulus and density of the rock massif. The most important parameters, however, are the geometric parameters, i.e., the depth and diameter (the size) of underground structures. According to Dowding and Rozen (1978), damage to shallow tunnels due to earthquakes occurs upon the excess of the certain value of acceleration (ground velocity) measured on the surface. The "no damage" limit lies below the level of 1.9 m.s-2 (approx. 0.2 m.s-1); the level of lesser damage lies in the range of 1.9 m. s-2 (approx. 0.2 m.s-1) to 5.0 m.s-2 (approx. 0.91 m.s-1). The authors consider the values of the influence of vibrations in shallow underground areas as about half the value measured on the surface. Then the limit values for underground spaces are approximately 0,9 m.s-2 (0,1 m.s-1) for no damage zones, and limit values for lesser damage in the range of 0,9 m.s-2 (0,1 m.s-1) to 2,5 m.s-2 (0,45 m.s-1). Singh (2002) documents different limit values for the occurrence of damages in a mine as a result of vibrations induced by blasting explosives on the surface. According to this study, the first damage can arise after reaching a ground velocity of 0.05 m.s-1 in rocks of very poor quality (RMR = 20 - 30). Different limit values refer to different underground structures and different sources of vibration, i.e., particularly to the frequency range of vibrations, local geological pattern, the shape and geometry of the underground spaces, reinforcement of underground structures and other parameters. Model experiments in various underground structures have shown that they are resistant to vibration. However, the existence of seismic discontinuity makes these structures exceptionally susceptible to collapse, especially in the case of shallow underground structures. Numerical modelling of the dynamic response of underground gas storage in caverns after the seismic load is stated in Wang et al. (2014). They use the modelling program FLAC3D, and they consider the size of the induced acceleration and the duration of vibrations as main factors. Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 301 New findings of the effect of technical vibrations As mentioned in the introduction, technical vibrations differ from natural earthquakes, as regards the comparable value of maximum vibration amplitudes, especially in the frequency range of the signal and mostly its duration. The most usual attribute of technical vibrations is that they are often repeated shocks or periodical signals. In case of corresponding damage of construction, it is necessary to take into account the fact that repeated load, even if it does not reach critical values, can seriously debase the technical conditions of the structures, especially if they are already fissured and/or cracked. In addition, it is necessary to consider higher frequencies, whether the generated frequencies do not match the eigenfrequency of some of the primary or secondary seismic members of the structure. Then, resonant vibration is generated, and a significant increase in the probability of cracks occurring is expected. The most intensive vibration effect is generated by a blast of explosives (Fig. 6). Blasts are represented by short but usually very intense impulses. As referred in ISO 4866 Standard, the frequency spectrum of the seismic records is continuous and includes frequencies ranging from lower values to very high values - usually 1 to 300 Hz. Wide frequency range of blasting depends on the properties of the disintegrated material, explosive properties, and blasting technology. The frequency spectrum of the seismic record of blasting is further significantly influenced by the environment, in which the waves pass through; higher frequency components are in the rock mass attenuated faster with increasing distances (for example, Barton, 2006; Banerjee and Kumar, 2016). Fig. 6. Blast in Dewon quarry, Jarnoltowek, Poland, 2012. (Photo: author). The evaluation of the effect of technical vibrations is usually based on measured values of ground velocity or acceleration; the maximum values can be calculated from empirical relations in some types of technical seismicity. To obtain experimental values, sensors are placed in the evaluated structures, either in cellars or on the lowest floor, and the enclosure load-bearing wall. Usually, the load of structures generated by blasting vibrations is evaluated according to the maximum ground velocity amplitude (or acceleration) and the frequency of the prevailing vibrations (for example, CSN 730040 – Czech Republic, STN EN 1998-1/NA/Z1 – Slovak Republic, DIN 4150 – Germany, PN-B02170:2016-12 – Poland …). An empirical relationship is formed which represents the dependence of the maximum ground velocity amplitude Vmax on the total weight of the charge (or the weight of the charge fired at the one-time stage) Q and distance l (for example, Dojčár et al., 1996; Tripathy et al., 2016). At a sufficient distance from the source of vibrations, the so-called Langefors (or also Koch) formula is used (in the general form) Zdeněk Kaláb: Influence of vibrations on structures 308  g gad a    , (3) where ad is dynamic acceleration [m.s-2] and g is gravitational acceleration [g = 9.80665 m.s-2]. The latter method is based on the method of partial coefficients used in the ultimate load design concept. This principle is commonly used in Eurocodes. The method of partial coefficients is based on the verifying in all design situations whether the values for limit states are not exceeded if the design values are assumed in all design models to be applied to the loading, material properties, and geometrical data. The partial coefficients are partially based on the theory of reliability and partially on historical and empirical experience. Problems of measurements and interpretation of vibrations originating at small distances during shallow tunnel excavation are paid great attention, first of all in settled areas (for example, Qui et al., 2008; Kaláb et al., 2011). Special attention is even devoted to the impact of vibration on vibration-sensitive devices. Conclusion Influences of earthquakes and quarry blasts on the structure are traditionally discussed and solved. Presently, vibrations generated by commercial explosives in tunnel construction may cause structural damage in urban areas. Therefore, suppressing the vibration effects and mitigating the possible hazard after blasting is important. The duration and also the number of explosives were carefully controlled. Urban tunnel construction induces not only changes in rock massif, but buildings and inhabitants in the nearest surroundings above a tunnel or underground working can be affected too. At present, permanent seismic monitoring with automatic data acquisition and primary interpretation of basic parameters is favoured in urban regions when significant vibrations are generated. Realisation of temporary seismic stations that will operate in suitable buildings during the whole period of seismic loading (generally weeks or first months) is supposed. Obtained results are at disposal to civil engineers, fire-fighters and also to custodians and occupants of influenced buildings. Usually, the web application is used with different access authority levels. Generally, it is necessary to point out that disturbed objects, even without visible signs (for example, cracks), are more vulnerable. It is reflected by the resonance vibration of the smaller or larger building element and the acceleration of the "ageing" of the object. It is appropriate to include this fact in the assessment of a load of a structure by means of a coefficient (similar use as a construction reliability factor) if the discussed effect is proven by the passporting of the structure. This paper summarises common information about the influences of vibrations on structures. The paper shows differences of vibration evaluation for earthquakes and technical events, esp. blasts. Examples of real wave patterns document common shapes (Fig. 8 and Fig. 9) and also signals with significant resonant vibrations (Fig. 10 and Fig. 12). Also, the wave field of high frequencies of seismic signal significantly interferes on the surface, and an important part of this field is also a response of the buildings’ constructional elements. Acknowledgement: The paper has obtained financial support for conceptual development of science, research and innovation in 2018, assigned to VSB-Technical University of Ostrava, The Ministry of Education, Youth and Sports in the Czech Republic. This research is partly sponsored by Research Program of Academy of Sciences of the Czech Republic, OZ30860518. References Ali A., Abu-Hayah N., Kim D., Cho G. S. (2017) Design response spectra-compliant real and synthetic GMS for seismic analysis of seismically isolated nuclear reactor containment building. Nuclear Engineering and Technology, 49, 4, 825-837, https://doi.org/10.1016/j.net.2017.02.006 Banerjee S., Kumar A. (2016) Determination of seismic wave attenuation: A Review. Disaster Advances, 9 (6), 10-27. Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 309 Barton N. (2006) Rock quality, seismic velocity, attenuation and anisotropy. CRC Press, Taylor & Francis Group. Båth M. (1979) Introduction to seismology. Birkhauser Verlag, Basel. Berr G. – ed. (2003) Numerical simulation in tunnelling. Springer. Bolt B.A.: Earthquakes. W. H. (1999) Freeman and Company, New York, fourth ed.. Bongiovanni G., Buffarini G., Clemente P., Rinaldis D., Saitta F. (2017) Experimental vibration analyses of a historic tower structure. J Civil Struct Health Monit, Vol. 7, 601–613. DOI 10.1007/s13349-017-0245-4 Bongiovanni G, Buffarini G, Clemente P, Saitta F. (2014) Dynamic characterization of the Trajan’s Column. In: Pen˜a F, Cha´vez M (eds), Structural analysis of historical constructions. Proc. SAHC2014, Mexico City. Bullen K.E., Bolt B.A. (1985) An Introduction to the Theory of Seismology. Cambridge University Press, Cambridge 4th edition. Bulyčev H.C. (1982) Mechanics of underground objects. NEDRA, Moscow. Clemente P., Bongiovanni G., Buffarini G. (2002) Experimental analysis of the seismic behaviour of a cracked masonry structure. Proc. of 12th European conf. on earth. eng. (12ECEE, London), Elsevier Science Ltd. Dojčár O., Horký J., Kořínek R. (1996) Blasting technology. Montanex, a.s., Ostrava. Dowding CH, Rozen A (1978): Damage to rock tunnels from earthquake shaking. J Geotech Eng Div, 104, 15–20. Doyle H. (1995) Seismology. John Wiley & Sons Ltd., Chichester. Chakraverty S., Sahu A., Keong Ch.K., Hassan S.M. (2012) Recent trends of computational methods in vibration problems. Advances in Acoustics and Vibration, Vol 2012, http://dx.doi.org/10.1155/2012/645981. Chudley R., Greeno R. (2014) Building Construction Handbook. Routledge, Taylor & Francis Group, eleven ed.. http://www.simardartizanfarm.ca/pdf/Building_Construction_Handbook.pdf Graizer V. (2006) Equation of pendulum motion including rotations and its imlifications to the strong-motion. In: Teisseyre R., Takeo M., Majewski E. – eds: Earthquake source symmetry, structural media and rotation effects. Springer-Verlag, Berlin, 471-485. Gupta A. K. (1992) Response spectrum method in seismic analysis and design of structures. CRC Press, Taylor & Francis Group. Hori M. (2006) Introduction to computational earthquake engineering. Imperial College Press, London. Hu J., Xie L (2004) Variation of earthquake ground motion with depth. Acta Seismologica Sinica, 18, 1, 72-81, DOI 1000-9116(2004)01-0072-10. Iervolino I., Maddaloni G., Cosenza E. (2008) Eurocode 8 compliant record sets for seismic analysis of structures. Journal of Earthquake Engineering, 12, 54–90, http://www.reluis.it/doc/pdf/AccelerogrammiEC8/Eurocode_8_Compliant_Real_Record_Sets_for_Seismic _Analysis_of_Structures.pdf Isaac I.D. (1991) Effect of constructional vibrations upon an urban environment. In: Earthquake, blast and impacts: Measurements and effect of vibration. Elsevier Applied Science, 442-462. Johnson A.P., Hannen W.R. (2015) Vibration limits for historic buildings and art collections. Journal of Preservation Technology, Vol. 46:2-3, 66-74. Kaláb Z. (2004) Impact of seismicity on surface in mining affected areas: General description. Acta Geod. Geomat., Vol. 1. (133), 35-39. Kaláb Z. (2007) Shallow underground construction and vibration. Tunnel. Magasine of the CTC and STA ITA/AITES, 2, 16, 12-20. Kaláb Z., Knejzlík J. (1999) The influence of basinal structures on the shape of wave patterns of induced seismic events: An example from the North Bohemian Brown Coal Basin. Bulletin of the Czech Geological Survey, 74/2, Prague, 185-190. Kaláb Z., Knejzlík J., Lednická M. (2013) Application of newly developed rotational sensor for monitoring of mining induced seismic events in the Karvina region. Acta Geodyn. Geomater., Vol. 10, No. 2(170), 197205. http://www.irsm.cas.cz/materialy/acta_content/2013_02/acta_170_09_Kalab_197-205.pdf Kaláb Z., Lednická M. (2016) Long-term geomechanical observation in the Jeroným Mine. Acta Geophysica, 64, 5, 1513-1524, DOI: 10.1515/acgeo-2016-0054. Kaláb Z., Lednická M., Knejzlík J., Telesca L. (2010) First results from long-term monitoring of distance using a laser distance meter in shallow medieval mine. Acta Geodyn. Geomater., 7, 4 (160), 469-475. Kaláb Z., Lednická M., Kaláb T., Knejzlík J. (2015) Evaluation of vibration effect in shallow mine caused by natural and technical seismicity. 15th International Multidisciplinary Scientific Geoconference SGEM 2015, Albena, Bulgaria, Conference proceedings, Science and Technologies in Geology, Exploration and Mining, III, 855 – 862. DOI: 10.5593/sgem2015B13 Kaláb Z., Pandula B., Stolárik M., Kondela J. (2013) Examples of law of seismic wave attenuation. Metalurgija, 52, 3, 387-390. http://public.carnet.hr/metalurg/Metalurgija/2013_vol_52/No_3/MET_52_3_387390_Kalab.pdf Zdeněk Kaláb: Influence of vibrations on structures 310 Kaláb Z., Stolárik M., Kukutsch R., Němeček J. (2011) Olbramovice Tunnel – Experimental seismic measurements in a near zone. Tunnel - Magazine of the Czech Tunnelling Association and the Slovak Tunnelling Association ITA-AITES, Vol. 20, No. 1/2011, 93-99. Knejzlík J., Kaláb Z., Lednická M., Staš L. (2011) Investigation of the medieval Jeroným Mine stability: Present results from a distributed measurement network. In Idziak, A.F., Dubiel, R. – editors: Geophysics in Mining and Environmental Protection. Ser. Geoplanet: Earth and Planetary Science, Vol. 2, 59-70. DOI 10.1007/978-3-642-19097-1. Knejzlík J., Kaláb Z., Rambouský Z. (2012) Concept of pendulous S-5-S seismometer adaptation for measurement of rotational ground motion. Journal of Seismology, Vol. 16, No. 4, 649-656. DOI 10.1007/s10950-012-9279-6. Kondela J., Pandula B. (2012) Timing of quarry blasts and its impact on seismic effects. Acta Geodyn. Geomater., 9, 2(166), 155-163. Kulhánek O. (1990) Anatomy of Seismograms. Elsevier Science, Amsterdam. Lednická M., Kaláb Z. (2013) Vibration effect of earthquakes in abandoned medieval mine. Acta Geod Geophys., 48/3, 221-234,. DOI 10.1007/s40328-013-0018-4. Lednická M., Kaláb Z. (2015) Vibration response of waste rock dump in open pit mine caused by blasting operation. Acta Montanistica Slovaca, 20, 2, 71-79, http://actamont.tuke.sk/pdf/2015/n2/1lednicka.pdf Lednická M., Kaláb Z. (2016) Determination of granite rock massif weathering and cracking of surface layers in the oldest parts of medieval mine depending on used mining method. Arch. Min. Sci., 61, 2, 381-395. DOI 10.1515/amsc-2016-0028. Lednická, M., Kaláb, Z. (2016) Vibration effect of near earthquakes at different depths in a shallow medieval mine. Acta Geophysica, Vol. 64, No. 6, 2244-2263, 2016a. DOI 10.1515/acgeo-2016-0085 Lee W.H.K., Celebi M., Todorovska M.I., Igel H. (2009) Introduction to the special issue on rotational seismology and engineering applications. Bull. Seismol. Soc. Am., 99, 2B, 945-957. Lu Y. (2014) Structural vibration: Overview, modelling and evaluation. NTU Public Seminar. http://www.cee.ntu.edu.sg/NewsnEvents/EPres/Documents/Sem20Aug14/Structural%20vibrations_NTU%20pu blic%20seminar_LY.pdf, May 2018. Lyubushin A.A., Kaláb Z., Lednická M. (2014) Statistical properties of seismic noise measured in underground spaces during seismic swarm. Acta Geod Geophys., 49, 2, 209-224. DOI 10.1007/s40328-014-0051-y. Lyubushin A.A. (2007) Data analysis from geophysical and ecological monitoring. Nauka, Moscow. Lyubushin A.A., Kaláb Z., Lednická M. (2012) Geomechanical time series and its singularity spectrum analysis. Acta Geod. Geoph. Hung., Vol. 47, No. 1, 69-77. Macdonald A. J. (2001) Structure and architecture. Architectural Press, University of Edinburgh, second ed.. Merritt F. S., Ricketts J.T. (2001) Building design and construction handbook, The McGraw-Hill Companies, Inc., sixth ed. Owen G.N., Scholl R.E. (1981) Earthquake engineering of large underground structures. Report no. FHWA RD80 195. Federal Highway Administration and National Science Foundation. Pandula B., Jelšovská K. (2008) New criterion for estimate of ground vibrations during blasting operations in quarries. Acta Geodyn. Geomater., 5, 2(150), 147-152. Pandula B., Kondela J. (2010) Methodology of seismology of blasting operations. SSTVP, Banská Bystrica, Slovakia. Pratt H.R., Hustrulid W.A., Stephenson D. E. (1978) Earthquake damage to underground facilities. Savannah River Laboratory Report, DP-1513, 20-25. Qui W., Gong L., Zhang J., Hu H. (2008) Study on vibration influence on existed tunnel by blasting construction of underpass dispersion tunnel in short distance. Proceedings of World Tunnel Congress 2008, India, 11391147. Shearer P.M. (2009) Introduction to seismology. Cambridge University Press, Cambridge, second edition. Scherbaum F. (1994) Basic concept in digital signal processing for seismologists. Springer-Verlag. Serati M., Moosavi M. (2010) Analysis of influencing factors in response spectrum of underground structures using numerical method. In: Rock stress and earthquakes, Proceedings of the Fifth International Symposium on In-situ Rock Stress. 5th International Symposium on In-situ Rock Stress and Earthquakes, Beijing, China, 579-583. Singh P.K. (2002) Blast vibration damage to underground coal mines from adjacent open-pit blasting. Int J Rock Mech Min Sci., 39, 959–973. Spathis A. T., Noy M. J. – eds. (2010) Vibrations from Blasting. CRC Press, Taylor& Francis Group. Teisseyre R., Takeo M., Majewski E. – eds (2006) Earthquake source asymmetry, structural media, and rotation effects. Springer-Verlag, Berlin. Towhata I. (2008) Geotechnical earthquake engineering. Springer, Verlag Berlin Heidelberg. Acta Montanistica Slovaca Volume 23 (2018), number 3, 293-311 311 Tripathy G. R., Shirke R. R., Kudale M. D. (2016) Safety of engineered structures against blast vibrations: A case study Journal of Rock Mechanics and Geotechnical Engineering, 8, 2, 248-255, DOI: 10.1016/j.jrmge.2015.10.007 Udías A. (1999) Principles of seismology. Cambridge University Press. Varnusfaderani M.G., Golshani A., Nemati R. (2015) Behavior of circular tunnels crossing active faults. Acta Geodyn. Geomater., 12, 4 (180), 363–376. DOI 10.13168/AGG.2015.0039 Villaverde R. (2009) Fundamental concept of earthquake engineering. CRC Press, ninth ed., Taylor & Francis Group. Viskup J., Pandula B., Leššo I., Jelšovská K. (2005) Spectra of seismic response. Acta Montanistica Slovaca, 10(2005), 2, 380-386. Wang T., Yang Ch., Yan X., Li Y., Liu W., Liang Ch., Li J. (2014) Dynamic response of underground gas storage salt cavern under seismic loads. Tunnelling and Underground Space Technology, 43, 241–252. Zeigler J.M. (2018) Vibration and damage. http://vibrationdamage.com/vibration_and_damage.htm, May 2018.