Lecture 2 s.s. iii continuare Design of Steel Structures - Faculty of Civil Engineering Iaşi

Lecture 2
continuare
STEEL INDUSTRIAL BUILDINGS
C.Teleman.StelStructuresIII.
Lecture2cont.
1

SteelIndustrialBuildings
SPECIFIC BUILDINGS FOR
INDIVIDUAL PROCESSES
UNIVERSAL (FLEXIBLE)
DESTINATIONS
steelworks with Martin kilns or with
converters, rolling mills, workshops for
coke production, etc.
various kinds of industrial activities
developed or modified/changed during
the service life of the building:
workshops, wear-houses, showrooms.
1. CLASSIFICATION
2. SPECIFIC FEATURES OF
INDUSTRIAL BUILDINGS
Regular shapes in plan:
- rectangular,
-oblong several rectangular interconnected.
- mono-pitched or duo-pitched roof in transversal plane
- small slopes of the roof: under 300
-single storey buildings (rarely two stories or more)
Plane shape of the industrial buildings: separation
in blocks between them tolerance distances being used

The type of the industrial building The limit braced block 1) The limit length of a building 2)
Heated 90 m 230 m
Non-heated and with exothermic processes 75 m 200 m
Trestle bridges (portal frames and conveying
bridge for outside activities)
50 m 130 m
Distances between the blocks of buildings
1) Limit braced block - the maximum distance between the end of the building and the axis of the
vertical bracing;
2) Limit length of a building - the maximum length of a building between two tolerance distances
along the building.
Position of the tolerances between blocks in the industrial buildings

• Observations
• Steel structures may adopt bigger tolerance distances than structures in
reinforced concrete, due to the superior characteristics of the steel.
Deformations are easier to be absorbed at the level of mechanical connections;
also, the cycles of loading having as a result the development of stresses in plastic
domain, safe from exploitation point of view, are consuming important quantities
of energy (high dissipative structures);
• Steel columns are placed at bigger distances and flexible enough to deform
under the variations of temperature;
• In the case of a structure that combines columns of reinforced concrete with
steel rafters or trusses, constructive conditions for the reinforced concrete
elements must be considered;
• For structures that carry steel crane girders tolerance distances must be
considered up to 120 m.
• Between two units (braced blocks = rigid blocks) the tolerance distances imposed
by the seismic provisions are 1…2 m.

• Transversal section of the industrial buildings
 The structure of the building is obtained from several transversal plane
frames having one or more spans placed at certain distances, named bays.
 Two running transversal frames determine the basic module of the building.
 Modern industrial buildings have an in plane layouts with dimensions
ranging from 10.00 m up to about 40.00 m for spans and 4.00 m up to 15.00
m for bays.
 The transversal frame is the main structural system of the building
consisting in columns and girders interconnected and its design depends on
the dimensions imposed by the technological processes - equipment,
devices and various systems for lifting and transportation both horizontally
and vertically inside the building.
• The roof of the industrial buildings are mono-pitched or double pitched,
the slope being usually small (3...5%).

StructuralSystemoftheSteel IndustrialBuildings
VARIOUS NON-STRUCTURAL ELEMENTS:
STEEL, MASONRY, AND GLASS ROOF DECKING;
WALLS SHUTTING MADE OF STEEL SHEETING OR SANDWICH PANELS
–TRANSVERSAL -THE SPAN
FRAMED STRUCTURE
- LONGITUDINAL - THE BAY
For buildings equipped with cranes the crane girders may be structural elements
STRUCTURAL ELEMENTS
COLUMNS
RAFTERS (STEEL GIRDERS OR ROOF TRUSSES)

ModernIndustrialSteelBuildings
HeavyorLightIndustry

StructuralSolutionsfortheTransversalFrame
c)-three spans frame equipped with travelling cranes;
d) two central spans frame with two auxiliary sides
frames with lower heights; e) -several transversal
frames
a)- one span with double pitch roof truss; b) central
double pitched frame with transversal skylight and two
side with mono-pitched frames
a b
c
d
e
Steel roof trusses for industrial buildings

Steel columns for industrial building:
a) simple sections and b) compound sections
1
Transversal frame for buildings equipped with crane
travelling on runway longitudinal girders: 1- crab
Top part of the steel columns with
two different sections

Different profile shapes of steel
sheeting used for roofing:
a)- corrugated; b)- with trough;
c)- deck trough; d) – deck trough
with tray; e) – build-up deck
The roof cladding may be placed directly on the top chord subjecting the bars to compressive
forces and bending moments; if the roof is heavy and/or the span and the bay are big the
stresses increase substantially. The design solutions are:
- to diminish the length of the bars at the top chord by introducing intermediary struts;
- to strengthen the cross sections of the bars at the top chord to cope with combined
stresses from N and M including the stability verifications.
In order to avoid these inconveniences we use purlins placed on the top chord in the
truss internal joints

Roof truss for wide spans and heavy loading:
a) constructive solutions;
b) hinged joint between truss and columna
b

LayoutandDesignoftheBracingSystem
ikff lll zy

ikfikf llll zy
 5,0;
a b c
braces designed only for tension braces designed to tension:
-if the braces are articulated in j:
-If the braces are not articulated in j:
-diagonal i’k’ is compressed and out of
service.
ikff lll zy

braces designed for compression
 Upon the transversal frame act horizontal and vertical loads in its plane; the frame is
not able to take loads normal to its plane, longitudinal to the building.
 The stiffness of the whole structure is insured by the longitudinal elements placed
between the plane frames.

The bracing system insures a spatial character and a corresponding stiffness and is
designed to provide the following requirements:
 a spatial collaboration between all the transversal frames,
 small deformations of the structure under horizontal transversal actions,
 stability during the assembling stage,
 reducing of the effective lengths of the structural elements in compression and
bending,
 taking over the horizontal loads due to wind actions and the surge effects due to
cranes.
The following structural elements are usually braced:
 the roof trusses;
 the skylight (if it exists and has relevant dimensions);
 the columns;
 the crane girders (if the building is equipped with cranes).

Braces for the roof truss
They divide themselves in the following distinct categories:
- horizontal longitudinal bracing at the bottom chord of the truss, their position
being along the structure in the external panels determined between the joint in the
supports of the trusses and the next joint by certain longitudinal elements (rods).
The destination of the horizontal bracing is to take the horizontal reactions from the
top part of the intermediary columns that carry the longitudinal walls. If the truss is
fixed to the column, then the bottom chord of the truss being in compression, has to be
provided with bracing in the second panel. The positions of the bracing in the case of
multi-spans structures when both the heights of the columns and the lift capacities of
the cranes have small or medium values are presented and also for big heights and
heavy lift capacities.
Bracing systems at the bottom chord of
the truss:
a) - ties are placed in the truss joints; b)-
ties are placed intermediary between the
truss joints; 1- transversal bracing; 2-
longitudinal bracing; 3-ties

Longitudinal bracing system in the plane of the roof:
1- at the top; 2- at the bottom; 3- intermediary column
- horizontal longitudinal bracing at the top chord of the truss, are mostly used for the
case when the height of the columns and the lift capacities are small. They are placed in the
same positions only they are part of the roofing system as plane lattice girders, their flanges
being the purlins.
If the roofing system is not able to sustain wind action alone, then the following conditions
are necessary to be verified:
HLw
2
1
W
10
L
b;m5.2b
T
T


 The longitudinal horizontal bracing of the
truss reduce the deformations of the
structure at the roof level from the effect of
the important horizontal transversal loads.
 The static scheme for design of the
horizontal longitudinal bracing is a
continuous lattice girder, the internal
supports being the structural joint of the
transversal frame between the column and
the rafter.

Different layouts of the bracing system at the
top and bottom chord of trusses: a) braces in
the boom in case of fixed connection between
the truss and the column; b) braces in case of
light cranes and small heights
a b
- horizontal transversal bracing from the bottom and the top chord of the truss are
placed normal to the longitudinal axis of the structure, in its end bays, also in the bays
next to the tolerance distance between adjacent blocks and at every 50...60 m along the
structure. Some of the purlins are parts of the system of horizontal bracing (under the
skylight the purlins are missing so rods have to be placed).
The role of horizontal transversal bracing at the bottom chord of the truss is to insure its
lateral stability.
The bracing system at the top chord of the truss takes the horizontal reactions coming
from the top of the intermediate columns of the gable walls (reactions coming from the
wind action on gable)

Design of the internal members of the horizontal transversal bracing
In design and computation of internal forces the
bracing system is assimilated with a lattice girder
with parallel chords.
-vertical bracing of the marginal and central struts of the truss are placed in the bays
containing horizontal transversal bracing and intermediary at 3-5 bays along the structure
(in order to insure the stability during the assembling stage).
They may also be placed under the supports of the skylight and in the case of the overhead
travelling cranes at the joints of the bottom chord of the truss.

Vertical bracing system of the struts of the truss: marginal and central

Braces of the columns:
- Vertical bracings of the columns are placed in the axis of the columns longitudinally
along the structure. In the end bays, temperature effects must be taken into account and
only a flexible rod is placed at the top part of the column. Generally, the bracing is placed
both at the top and at the bottom part of the column in a bay situated in the middle of
the longitudinal axes, or if the building is long, at L/3, L being the longitudinal
dimension.
- horizontal bracings of the columns are used in the case when the bays are very big their
purpose being mainly to reduce the effective length of the intermediary columns
belonging to the structure of the longitudinal walls; they also transfer a part of the
horizontal forces due to wind action on walls to the structural columns.
In choosing the cross sections of the bracings the governing verification relationship is
for limit slenderness, their cross sections resulting rather small.
    0LVhFW;0M TipA 
     tgFW
L
h
FWV p
T
i
p

Lecture 2 s.s. iii continuare Design of Steel Structures - Faculty of Civil Engineering Iaşi

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Lecture 2 s.s. iii continuare Design of Steel Structures - Faculty of Civil Engineering Iaşi