دورات هندسية

 

 

Nature and Consequences of Settlement

النتائج 1 إلى 1 من 1
  1. [1]
    tafatneb_dichar
    tafatneb_dichar غير متواجد حالياً

    عضو فعال جداً

    تاريخ التسجيل: Aug 2007
    المشاركات: 331
    Thumbs Up
    Received: 2
    Given: 0

    Nature and Consequences of Settlement

    Nature and Consequences of Settlement
    by Donald O. Dusenberry, P.E.
    Structural settlement normally occurs when the foundation is inadequate to support
    the loads applied to a structure. Settlement can occur if a foundation is inadequately
    designed or installed, or if conditions unforeseen during design affect the
    structure during its life. Certainly, settlement can occur if, due to changes in use,
    loads on a foundation exceed those envisioned by the designer. However, excavations
    near existing foundations can cause settlement as well. Changes in groundwater
    elevation can cause consolidation that can affect foundations. Bridge piers
    in rivers can be undermined by scour of foundation materials below footings.
    Decay of organic materials below footings can cause volume changes in the foun-
    dation materials. In most cases, the reasons for settlement are best determined by
    a thorough geotechnical investigation and assessment.
    Settlement causes distortions that affect the function of a structure, stresses that
    can damage structural members and their connections, cracking of structural elements,
    overloads in structural elements that acquire extra load due to distortions
    of indeterminate structural systems, and damage to architectural components.
    Usually when settlement is severe enough to cause significant distress in conventional
    buildings, its manifestation is readily visible.
    Determination of Settlement Loads
    As with self-straining loads, loads due to settlement are the result of internal
    restraint of movement, rather than from an externally applied load. Structures that
    are fully pinned theoretically can be subjected to settlement without developing
    stresses. However, since few practical structures are without restraint, structures
    generally become stressed when settlement occurs.
    The analysis of settlement effects is best begun with a survey of the building to
    measure its distortion. Care must be taken to obtain accurate data on relevant
    structural elements.
    Data points must be selected to be representative of the movements of the structure.
    Normal deformations due to beam flexure, for instance, must be excluded
    from settlement deformation analyses. Data collected on architectural features
    that are not locked fully with the structural system, such as wood trim or column
    boxing, may not reflect structural movements accurately.
    Useful places to acquire data are the tops of column baseplates, because these
    elements usually are installed at elevations close to those specified. Differences
    in elevations of the tops of structural steel at various places on any level of the
    building usually are reliable indications of settlement amounts. When the floor
    system is concrete slab, analysis of the patterns of elevation differences, as measured
    on the top of slabs next to columns over several floor levels, can reveal settlement
    amounts.
    The investigation must establish whether the original, as-built positions can be
    determined with sufficient certainty. Normal construction tolerances allow floor
    surfaces, for instance, to vary from specified elevations. Data should be assessed
    with consideration to the possibility that data points were not precisely at specified
    elevations, but within tolerances. Furthermore, it is common for buildings to
    be erected out of level or out of plumb.
    If an as-built survey was performed at the time of construction, it can be used
    to compare to the data collected during the investigation. The investigator must
    assess the precision with which field surveys are performed so that measurement
    errors do not unduly affect judgment about settlement. When high precision is
    required, such as when movements are to be monitored over time, special survey
    instruments and procedures are needed to achieve the required precision.
    LOADS AND HAZARDS: THEIR NATURE, MAGNITUDE, AND CONSEQUENCES
    Sometimes useful information can be obtained by observing the architectural
    and structural features of the building. For instance, mortar joints in masonry construction
    usually are constructed relatively straight and level.
    Once the amount of settlement is known, the load effects on the structure must
    be determined by analysis. Reliable models must represent the behavior of the
    structure as it is deformed. Using these reliable models, forces in structural elements
    can be evaluated by imposing the measured support movements. Care must
    be taken to ensure that the model adequately represents connection stiffness and
    the potential for bearing points or connections to slip under load. Furthermore, if
    structural materials are susceptible to stress relaxation, these effects must be considered
    when determining the residual forces in members.

  
الكلمات الدلالية لهذا الموضوع

عرض سحابة الكلمة الدلالية

RSS RSS 2.0 XML MAP HTML