I. INTRODUCCIÓN
2.2. Bases teóricas de la investigación
2.2.12. La jurisdicción
2.2.1.16. Las partes procesales en proceso penal
When modelling column elements within an FE model, consideration should be given to the following points:
When a column changes dimensions between two successive levels, the model should take into account the corresponding offsets in the column centre lines or it may neglect the associated bending moment induced within the column. This situation is common in faÇade columns, whose dimensions reduce towards the top of a structure and where the faÇade face is continuous.
Where ‘walking columns’ are used, the offset of the columns can be significant and will induce significant lateral forces with the floor elements.
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4.2.2 Column spacing
The spacing of columns within the footprint of the building is determined incollaboration with clients and architects. Columns will be positioned to facilitate ease of layout for the appropriate use of the floor spaces. Due to the size of the columns in tall buildings, it is not normally possible to conceal them within walls, as is common practice in low-rise construction. Adjustment of column layout should be kept to a minimum, as each change in plan position requires some form of transfer structure, which can be expensive, slow the construction rate and occupy more depth than a typical floor plate.
Column spacing is generally kept in the range of 6-10m, as this produces economical column sizes and floor depths whilst maintaining usable floor plates. Wider spacing is generally more suitable for office use, with smaller spacing acceptable for residential purposes. Should the building use change through the height of the building, a single transfer floor may be appropriate and can generally be assigned for plant and equipment or as part of the building’s stability system.
A small adjustment in column locations, floor-on-floor, can be achieved by using
‘walking columns’ stepping the column positions incrementally over a number of floors to achieve the overall desired offset. See Figure 4.1.
The eccentricity of the vertical loading at each floor is resisted by tension and compression forces within the floor structures. Floors, therefore, become part of the vertical load carrying system and, in addition to gravity loadings, must be designed and reinforced to resist additional lateral loadings and treated appropriately in terms of their response to accidental loadings, robustness and disproportionate collapse.
Column spacing at the perimeter of the building can be influenced by the selected façade. In modern buildings an open façade is often provided and columns centres are maximised for the least intrusion into the façade line and views for the building occupants.
Tension
Compression Walking
column Eccentricity in column
compression transferred through floors to core Figure 4.1
‘Walking columns’.
4 Structural elements
Often, a short cantilever slab is provided at the building perimeter, allowing the façade to run past the outer columns in an uninterrupted line. This can simplify and regularise the details for the façade and help with the detailing of the column/floor slab connection.
If the outer columns of the building are utilised as part of the lateral load carrying system - for example, in a framed-tube structure - column spacing will be much smaller (perhaps 2-4m) and the slab edge will be formed with the stiff interconnecting beams.
4.2.3 Column sizes
The initial sizing of columns will take into account the following factors: Axial and bending stresses
Slenderness, particularly for very tall columns (entrance areas, double height spaces)
Fire resistance and, hence, cover requirements, particularly for columns using high-performance concrete - guidance is provided in most national codes
Structure robustness criteria.
When sizing the columns in tall buildings, the designer should also consider the following factors:
Obtaining uniform stress levels across the columns and walls in a single floor plate in order to reduce differential shortening effects.
Being mindful of changing concrete strength too abruptly - for example, a floor made of C40 concrete located between two columns using C80 concrete may cause problems.
Being aware of differential temperature effects on façade columns exposed to direct sunlight.
Common column shapes are compared in Table 4.2.
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Table 4.2 Comparison of common column shapes
Column shape Technical
feasibility Economy Ease Of
planning Overall
rating Comments
A regular and compact shape, convenientto accommodate. Forming shape can be more expensive.
Circular
The most relevant shape to resist bending effects; also the easiest one to construct.
A regular and compact shape which is very convenient to accommodate.
Square
b
h
Strength influenced by slenderness for smaller side dimension. A regular and compact shape which is convenient to accommodate.
Rectangle b:h < 3:1
b
h
Strength influenced by slenderness for smaller side dimension. Likely to attract lateral loading and hence may need to be considered as a shear wall. Can be convenient in structures where cross walls suit the intended use.
Rectangular b:h > 3:1
Key to ratings:- - Poor - Good - Excellent
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4.2.4 Vertical loading and
The compression stresses applied to columns can quickly be determined by carrying outhorizontal forces
a floor-by-floor ‘manual’ vertical load take down, assigning the floor area supported by each column. Increases should be added for the continuity of floor structures. Manual load distribution techniques can also approximate the stresses generated from lateral loadings.Another vertical-load take-down comes from the analysis model for the entire building.
It is good practice to use both manual and computer techniques, as this provides a good insight into the load paths through the structure and also acts as a good method of verifying that the analysis results are correct.