Component longevity in terms of operation performance and resistance to deleterious forces :

Building science is the collection of scientific knowledge and experience that focuses on the analysis and control of the physical phenomena affecting buildings and architecture.[1] It traditionally includes the detailed analysis of building materials and building envelope systems. In Europe, building physics is a term used for the knowledge domain that overlaps heavily with building science,[2] and includes fire protection, sound control, and daylighting as well as the heat and moisture concerns that tend to dominate North American building science. The practical purpose of building science is to provide predictive capability to optimize building performance and understand or prevent building failures.Building science is the architectural-engineering-construction technology discipline that concerns itself with the 'mainly detail-design' of buildings in response to naturally occurring physical phenomenon such as: the weather (sun, wind, rain, temperature, humidity), and related issues:e.g. freeze/thaw cycles, dew point/frost point, snow load & drift prediction, lightning patterns etc. subterranean conditions including (potential for seismic or other soil + ground-water activity, frost penetration etc.). characteristics of materials,(e.g. Galvanic corrosion between dissimilar metals, permeability of materials to water and water vapor, construct-ability, compatibility, material-adjacency and longevity issues). characteristics of physics, chemistry and biology such as capillary-action, absorption, condensation ("will the dew point occur at a good or bad place within the wall?"), gravity, thermal migration/transfer (conductivity, radiation and convection), vapor pressure dynamics, chemical reactions (incl. combustion process), adhesion/cohesion, friction, ductility, elasticity, and also the physiology of fungus/mold. human physiology (comfort, sensory reaction e.g.radiance perception, sweat function, chemical sensitivity etc.). energy consumption, environmental control-ability, building maintenance considerations, longevity/sustainability, and occupant (physical) comfort/health.The building science of a project refers to strategies implemented in the general and specific arrangement of building materials and component-assemblies.The practical outcome of building science knowledge is reflected in the design of the architectural details of the building enclosure (see building envelope), and ultimately in the long-term performance of the building's 'skin'. The scope can be, and is, much wider than this on most projects; after all,engineering is applied science mixed with experience and judgement. When architects talk of "building science", they usually mean the 'science' issues that traditional engineering disciplines traditionally avoided, albeit there are emerging disciplines of 'building scientists', 'envelope consultants', and 'building engineers'.Many aspects of building science are the responsibility of the architect (in Canada, many architectural firms employ an architectural technologist for this purpose), often in collaboration with the engineering disciplines that have evolved to handle 'non-building envelope' building science concerns: Civil engineering, Structural engineering, Earthquake engineering, Geotechnical engineering, Mechanical engineering, Electrical engineering, Acoustic engineering, & fire code engineering. Even the interior designer will inevitably generate a few building science issues.Building design

Earthquake/seismic DesignAll kinds of structures are projected according to two strain conditions: static and dynamic. The static ones are tied to the structures dead loads added to the so-called live loads (of people, furniture, etc.), the dynamic ones are tied to the natural, abnormal, and artificial movements (earthquake and loads wind) the structure can sustain during its life cycle. The parameters which characterize structure dynamics are tied to the geometry of the building and to the physical and mechanic properties of its composition. The parameters are:- The fundamental frequency of vibration (f) and the respective oscillation period (T=1/f) (see oscillation frequency);- The equivalent dumping coefficient (neq);- The mode shape (the way in which the structure buckles);The first parameter varies according to the structure stiffness; very tall and then very flexible buildings as skyscrapers (low oscillation frequencies) oscillate slowly with respect to lower and squat buildings, and according to the building mass. The second parameter takes into account all the dissipation phenomena tied to the viscosity of materials and to friction phenomena. The mode shape describes the way of deformation which the structure is subjected to during the seismic event, and highlights whether or not the structures presents a good seismic behavior.Reducing the effect of earthquakes on buildingsBy monitoring the response of structures subject to earthquakes and by applying new knowledge and technologies, scientists and engineers continuously develop design and repair techniques on buildings, so that their ability to control the earthquake effects will grow. In order to reduce the destructive effects of earthquakes both on new-built buildings and especially on older ones, there exist some seismic adjustment techniques, with the aim of reducing the strain effects that earthquake causes. These techniques can be divided into two different categories:Base isolation: it is aimed to untie the ground-foundation system, so that the structure can be seen as it is floating on the ground during the seismic event, thus reducing the strains.Dissipation systems: there exist various types of dissipation systems, but they all have in common the effect of increasing the previously seen viscous dissipation coefficient of the structure. The better known base isolation technique consists of inserting some special equipment (isolator (building design)) in the proximity of foundations. This equipment offers a high stiffness for vertical loads so that the structure is not subject to sinking, while offering a low stiffness for horizontal ones, which are peculiar of seismic events. This way all seismic effects are absorbed by the equipment, whereas the structure is subject to low oscillations and consequently to low strains.The dissipation systems (dissipator (building design)) are made by a series of devices inserted on the inside of the building frame using different techniques, with the aim of slowing down the structure oscillation and dispelling seismic energy.Energy Efficiency In the US contractors certified by the independent organization Building Performance Institute advertise that they operate businesses as Building Scientists. This is questionable due to their lack of scientific background and credentials. This is true in Canada for most of the Certified Energy Advisors.Indoor environmentBuilding indoor environment covers the environmental aspects in the design, analysis, and operation of energy-efficient, healthy, and comfortable buildings. Fields of specialization include architecture, HVAC design, thermal comfort, indoor air quality (IAQ), lighting, acoustics, and control systems.Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure's integrity. Base isolation is one of the most powerful tools of earthquake engineering pertaining to the passive structural vibration control technologies. It is meant to enable a building or non-building structure to survive a potentially devastating seismic impact through a proper initial design or subsequent modifications. In some cases, application of base isolation can raise both a structure's seismic performance and its seismic sustainability considerably. Contrary to popular belief base isolation does not make a building earthquake proof.Base isolation system consists of isolation units with or without isolation components, where:1. Isolation units are the basic elements of a base isolation system which are intended to provide the aforementioned decoupling effect to a building or non-building structure.2. Isolation components are the connections between isolation units and their parts having no decoupling effect of their own.Advanced Earthquake Resistant Design TechniquesIntroductionThe conventional approach to earthquake resistant design of buildings depends upon providing the building with strength, stiffness and inelastic deformation capacity which are great enough to withstand a given level of earthquakegenerated force. This is generally accomplished through the selection of an appropriate structural configuration and the careful detailing of structural members, such as beams and columns, and the connections between them.

(fig. 1)In contrast, we can say that the basic approach underlying more advanced techniques for earthquake resistance is not to strengthen the building, but to reduce the earthquakegenerated forces acting upon it. Among the most important advanced techniques of earthquake resistant design and construction are base isolation and energy dissipation devices.Base IsolationIt is easiest to see this principle at work by referring directly to the most widely used of these advanced techniques, which is known as base isolation. A base isolated structure is supported by a series of bearing pads which are placed between the building and the building's foundation.(See Figure 1) A variety of different types of base isolation bearing pads have now been developed. For our example, we'll discuss leadrubber bearings. These are among the frequentlyused types of base isolation bearings. (See Figure 2) A leadrubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle of the bearing is a solid lead "plug." On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.Earthquake Generated Forces

(fig. 2)To get a basic idea of how base isolation works, first examine Figure 3. This shows an earthquake acting on both a base isolated building and a conventional, fixedbase, building. As a result of an earthquake, the ground beneath each building begins to move. In Figure 3, it is shown moving to the left. Each building responds with movement which tends toward the right. We say that the building undergoes displacement towards the right. The building's displacement in the direction opposite the ground motion is actually due to inertia. The inertial forces acting on a building are the most important of all those generated during an earthquake.It is important to know that the inertial forces which the building undergoes are proportional to the building's acceleration during ground motion. It is also important to realize that buildings don't actually shift in only one direction.Because of the complex nature of earthquake ground motion, the building actually tends to vibrate back and forth in varying directions. So, Figure 3 is really a kind of "snapshot" of the building at only one particular point of its earthquake response.

(fig. 3)In addition to displacing toward the right, the unisolated building is also shown to be changing its shape from a rectangle to a parallelogram. We say that the building is deforming. The primary cause of earthquake damage to buildings is the deformation which the building undergoes as a result of the inertial forces acting upon it. The different types of damage which buildings can suffer are quite varied and depend upon a large number of complicated factors. But to take one simple example, one can easily imagine what happens to two pieces of wood joined at a right angle by a few nails, when the very heavy building containing them suddenly starts to move very quickly the nails pull out and the connection fails. Response of Base Isolated BuildingBy contrast, even though it too is displacing, the baseisolated building retains its original, rectangular shape. It is the leadrubber bearings supporting the building that are deformed. The baseisolated building itself escapes the deformation and damagewhich implies that the inertial forces acting on the baseisolated building have been reduced.Experiments and observations of baseisolated buildings in earthquakes have been shown to reduce building accelerations to as little as 1/4 of the acceleration of comparable fixedbase buildings, which each building undergoes as a percentage of gravity. As we noted above, inertial forces increase, and decrease, proportionally as acceleration increases or decreases.Acceleration is decreased because the base isolation system lengthens a building's period of vibration, the time it takes for the building to rock back and forth and then back again. And in general, structures with longer periods of vibration tend to reduce acceleration, while those with shorter periods tend to increase or amplify acceleration. Finally, since they are highly elastic, the rubber isolation bearings don't suffer any damage. But what about that lead plug in the middle of our example bearing? It experiences the same deformation as the rubber. However, it also generates heat as it does so.In other words, the lead plug reduces, or dissipates, the energy of motioni.e., kinetic energyby converting that energy into heat. And by reducing the energy entering the building, it helps to slow and eventually stop the building's vibrations sooner than would otherwise be the case in other words, it damps the building's vibrations. (Damping is the fundamental property of all vibrating bodies which tends to absorb the body's energy of motion, and thus reduce the amplitude of vibrations until the body's motion eventually ceases.)Spherical Sliding Isolation SystemsAs we said earlier, leadrubber bearings are just one of a number of different types of base isolation bearings which have now been developed. Spherical Sliding Isolation Systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction.

(fig. 4)During an earthquake, the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally and vertically (See Figure 4.) The force needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also, by adjusting the radius of the bearing's curved surface, this property can be used to design bearings that also lengthen the building's period of vibration.For more information read this article titled Protective Systems for Buildings: Application of Spherical Sliding Isolation Systems as it describes one particular type of spherical sliding isolation system, and its successful use in making some structures more earthquake resistant.Energy Dissipation DevicesThe second of the major new techniques for improving the earthquake resistance of buildings also relies upon damping and energy dissipation, but it greatly extends the damping and energy dissipation provided by leadrubber bearings.As we've said, a certain amount of vibration energy is transferred to the building by earthquake ground motion. Buildings themselves do possess an inherent ability to dissipate, or damp, this energy. However, the capacity of buildings to dissipate energy before they begin to suffer deformation and damage is quite limited.The building will dissipate energy either by undergoing large scale movement or sustaining increased internal strains in elements such as the building's columns and beams. Both of these eventually result in varying degrees of damage. So, by equipping a building with additional devices which have high damping capacity, we can greatly decrease the seismic energy entering the building, and thus decrease building damage.Accordingly, a wide range of energy dissipation devices have been developed and are now being installed in real buildings. Energy dissipation devices are also often called damping devices. The large number of damping devices that have been developed can be grouped into three broad categories: Friction Dampers these utilize frictional forces to dissipate energy Metallic Dampers utilize the deformation of metal elements within the damper Viscoelastic Dampers utilize the controlled shearing of solids Viscous Dampers utilized the forced movement (orificing) of fluids within the damperFluid Viscous DampersOnce again, to try to illustrate some of the general principles of damping devices, we'll look more closely at one particular type of damping device, the Fluid Viscous Damper, which is one variety of viscous damper that has been widely utilized and has proven to be very effective in a wide range of applications. The article, titled Application of Fluid Viscous Dampers to Earthquake Resistant Design, describes the basic characteristics of fluid viscous dampers, the process of developing and testing them, and the installation of fluid viscous dampers in an actual building to make it more earthquake resistant. Damping Devices and Bracing Systems

(fig. 5)Damping devices are usually installed as part of bracing systems. Figure 5 shows one type of damperbrace arrangement, with one end attached to a column and one end attached to a floor beam. Primarily, this arrangement provides the column with additional support.Most earthquake ground motion is in a horizontal direction; so, it is a building's columns which normally undergo the most displacement relative to the motion of the ground. Figure 5 also shows the damping device installed as part of the bracing system and gives some idea of its action.