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UK
EUROCODES
Damascus University – Spring 2015
Instructor: Dr. Nachwan Khair
Lecture 2
‫‪UK‬‬
‫‪EUROCODES‬‬
‫جامعة دمشق – كلية الهندسة المدنية‬
‫الفصل الثاني من العام الدراسي ‪2014/2015‬‬
‫الدكتور المهندس نشوان الخاير‬
‫‪Lecture 2‬‬
Tension members
•A tension member
transmits a direct axial
pull between two points
in a structural frame
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In building frames, tension
members occur as:
• tension chords and internal
ties in trusses;
• tension bracing members;
• hangers supporting floor
beams.
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Examples of these members
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The main sections used for
tension members are:
• open sections such as angles,
channels, tees, joists, universal beams
and columns;
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The main sections used for
tension members are:
• closed sections. Circular, square and
rectangular hollow sections;
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The main sections used for
tension members are:
• compound and built-up sections. Double
angles and double channels are common
compound sections used in trusses. Built-up
sections are used in bridge trusses.
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Theoretically, the tension member is the most efficient structural element,
but its efficiency may be seriously affected by the following factors:
• The end connections. For example, bolt holes
reduce the member section.
• The member may be subject to reversal of
load, in which case it is liable to buckle
because a tension member is more slender
than a compression member.
• Many tension members must also resist
moment as well as axial load. The moment is
due to eccentricity in the end connections or
to lateral load on the member.
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End connections
Comments on the various types are:
• Bolt or threaded bar. The strength is
determined by the tensile area at the threads.
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End connections
Comments on the various types are:
• Single angle connected through one leg. The
outstanding leg is not fully effective, and if
bolts are used the connected leg is also
weakened by the bolt hole.
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Lecture 2
Design of tension members
The resistance of tension members is covered in
clause 6.2.3. The design tensile force is denoted
by Nt,Ed (axial design effect). In Eurocode 3,
similarly to BS 5950: Part 1, design tensile
resistance Nt, Rd is limited either by yielding of
the gross cross-section (to prevent excessive
deformation of the member) or ultimate failure
of the net cross-section (at holes for fasteners),
whichever is the lesser.
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Design of tension members
The Eurocode 3 design expression for yielding of
the gross cross-section (plastic resistance) is
therefore given as
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Design of tension members
And for the ultimate resistance of the net crosssection (defined in clause 6.2.2.2), the Eurocode
3 design expression is
The design tensile resistance is taken as the smaller of the
above two results. For ductility (capacity design), the design
plastic resistance of the gross cross-section should be less
than the design ultimate resistance of the net cross-section.
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Example: tension resistance
A flat bar, 200 mm wide and 25 mm thick, is to be used
as a tie. Erection conditions require that the bar be
constructed from two lengths connected together with
a lap splice using six M20 bolts, as shown in Figure.
Calculate the tensile strength of the bar, assuming
grade S275 steel.
Lap splice in
tension
member
with a
staggered
bolt
arrangement
Lecture 2
Example: tension resistance
Cross-section resistance in tension is covered in
clause 6.2.3, with reference to clause 6.2.2 for the
calculation of cross-section properties.
For a nominal material thickness (t = 25 mm) of less
than or equal to 40 mm the nominal values of yield
strength, fy, and ultimate tensile strength, fu, are
found from Table 3.1 to be 275 and 430 N/mm2,
respectively. Note that reference should be made to
the UK National Annex for the nominal material
strength.
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Example: tension resistance
The numerical values of the required partial factors
recommended by EN 1993-1-1 are γM0 = 1.00 and
γM2 = 1.25 (though for buildings to be constructed in
the UK, reference should be made to the National
Annex).
Gross area of cross-section
A = 25 × 200 = 5000 mm2
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Example: tension resistance
In determining the net area, Anet , the total area to
be deducted is taken as the larger of:
1. the deduction for non-staggered holes (A–A)
= 22 × 25 = 550 mm2
= 25 × (2 × 22 – 902/4 × 100)
= 594 mm2 (> 550 mm2)
Therefore, the net area of the cross-section
Anet = 5000 – 594 = 4406 mm2
2.
,
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Example: tension resistance
The design plastic resistance of the gross crosssection
Npl, Rd = 5000 × 275/1.00 = 1375 kN
The design ultimate resistance of the net crosssection
Nu, Rd = 0.9 × 4406 × 430 /1.25 = 1364 kN
The tensile resistance, Nt, Rd, is taken as the smaller of
Npl, Rd (1375 kN) and Nu, Rd (1364 kN).
Nt, Rd = 1364 kN
Note that for the same arrangement, BS 5950: Part 1 gives a tensile
resistance of 1325 kN.
Lecture 2
Angles with welded end
connections
Clause 4.13 of EN 1993-1-8
states that for an equal angle, or
unequal angle welded along its
larger leg, the effective area =
gross area.
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Angles with welded end
connections
The gross cross-sectional area of
an equivalent equal-leg angle of
leg size equal to that of the
smaller for an unequal-leg angle
connected by its smaller leg.
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Angles with welded end
connections
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Angles Connected by a
single row of bolts
Refer to EN 1993-1-8.
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Angles Connected by a
single row of bolts
For 1 bolt:
(3.11)
For 2 bolts:
(3.12)
For 3 or
more bolts:
(3.13)
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Angles Connected by a
single row of bolts
Values of reduction factors β2 and β3 can be found in Table 3.8:
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Tension Member Design Steps Summary
1. Determine the design axial load NEd
2. Choose a section
3. Find fy and fu from the product standards
4. Get the gross area A and the net area Anet
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Tension Member Design Steps Summary
5. Substitute the values into the equations
to work out Npl,Rd and Nu,Rd
(6.6)
(6.7)
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Tension Member Design Steps Summary
For angles connected by a single row of bolts, use the required equation to
work out Nu,Rd from EN 1993-1-8 which will depend on the number of bolts.
For 1 bolt:
(3.11)
For 2 bolts:
(3.12)
For 3 or
more bolts:
(3.13)
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Tension Member Design Steps Summary
6. The design tensile Resistance is the lesser
of the values of Npl,Rd and Nu,Rd
7. Carry out the tension check
N t , Ed
N t , Rd
 1.0
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(6.5)
‫مالحظة هامة‪:‬‬
‫يمنع الكتابة على الكود منعا ً‬
‫باتا ً وإضافة أي جداول غير‬
‫المصرح بها من قبل أساتذة‬
‫المقرر‪.‬‬
‫‪Lecture 2‬‬
Thank
you
Dr. Nachwan Khair
Lecture 2