Short answer
TBDY 2018 Chapter 10 divides the lateral load system of light steel buildings into sheathed panels and braced panels. Braced panels are Limited Ductility Level. Clause 10.4.2 gives member and connection rules, and 10.4.3 adds conditions for strap bracing: eccentricity moment, tensioned connections, foundations for amplified forces and bridging at most h/2 apart.
Key points
- Braced panels are a Limited Ductility Level system (10.2.1.2).
- Earthquake analysis uses the Equivalent Seismic Load Method with T = 0.2 s (10.2.6.1).
- In tension, brace strength is based on the gross section: AgFy/1.67 in ASD (GKT), 0.90 AgFy in LRFD (YDKT).
- Net section strength must be at least 1.20 times the brace design strength (Eq. 10.23).
- The screw pull-out strength is not used to resist earthquake loads.
In this article
Introduction
Chapter 10 of the Turkish Building Earthquake Code 2018 (TBDY 2018) is titled "Special Rules for the Design of Light Steel Building Structural Systems under Earthquake Effects". In the printed text it spans pages 218 to 242 and has three annexes: holes (Annex 10A), screw and bolt strength (Annex 10B), and panel tests (Annex 10C). This article reads the text in order, from the viewpoint of the braced panel.
Which class does a braced panel fall into?
Clause 10.1.2 divides lateral load-resisting systems into sheathed panels and braced panels. If the system contains hot-rolled steel members, the rules of Chapter 9 also apply. Clause 10.2.1 then gives the behavior class:
| Clause | System | Class |
|---|---|---|
| 10.2.1.1 | All earthquake effects are resisted by screwed or bolted OSB or plywood wall panels | High Ductility Level |
| 10.2.1.2 | All earthquake effects are resisted by braced panels or by gypsum-board sheathed panels | Limited Ductility Level |
The R and D factors and the permitted Building Height Classes are in Table 4.1 (10.2.1.3). So the choice of class directly affects the design load and the building height.
What is asked of the plan and storey layout?
Clause 10.2.1.4 asks for load-bearing panels to be placed as regularly as possible in plan, symmetrically or nearly symmetrically about the main axes, and to stack on top of each other in all storeys. This clause should be read at the start of design, because panel positions are the hardest thing to correct later.
Read nextLateral load path in a light steel building: from roof to foundation, step by stepWhat are the lower limits for material and screws?
- Minimum yield stress 235 MPa (10.2.3.2a).
- Ratio of tensile strength to yield stress at least 1.08 (b).
- Fracture elongation at least 10% for normal ductile and at least 16% for high ductile material (c).
- Normal ductile material only in purlins, facade girts and non-load-bearing studs (d).
- Connections use self-drilling screws or bolts; screws meet the torque and hardness values in Table 10.1 (f).
How is the earthquake analysis done?
According to 10.2.6.1, the Equivalent Seismic Load Method is used and T = 0.2 s is taken for the elastic design spectral acceleration. The equivalent seismic load is distributed according to the unit-length lateral load capacities of the sheathing materials or braced panels and their position in plan. The total shear demand on a storey is shared according to the relative capacities of the panels on that storey.
Clause 10.2.5.2 permits only one of ASD (GKT) or LRFD (YDKT) to be applied in design; for foundations only LRFD (YDKT) is used. The ASD (GKT) load combinations are given as G + 0.75Q + 0.75S + 0.75(0.7Ed) and 0.6G + 0.7Ed + H.
What does 10.4.2 require for a braced panel?
| Clause | What it says | On site |
|---|---|---|
| 10.4.2.1(a) | The chord studs to which the brace connects, the tracks and the connection members resist the forces amplified by the factor D | A chord stud is not calculated like an intermediate stud |
| 10.4.2.1(b) | In tension, strength is based on the gross section: ASD (GKT) AgFy/1.67, LRFD (YDKT) 0.90 AgFy. In compression, the stud equations are used | Strap and profile bracing are calculated separately |
| 10.4.2.1(c) | Net section check at the connection point: AnetFu ≥ 1.20 Pn,brace | Hole pattern and strap width are chosen together |
| 10.4.2.1(d) | The pull-out strength of screws is not used in the earthquake calculation | Screws are arranged to work in shear |
The factor 1.20 in Eq. 10.23 is not arbitrary. The text explains it as the ratio of the safety factors (2/1.67) and the strength reduction factors (0.9/0.75) used for the net section and the gross section.
Read nextGusset plates and strap end connections: how does force pass into the frame?What does 10.4.3 add for strap bracing?
| Clause | What it says | On site |
|---|---|---|
| 10.4.3(a) | If there are no straps on both sides of the panel, the moment T·e enters the stud calculation | With a strap on one face the stud is stressed more |
| 10.4.3(b) | Strap connections are made tight | Tension must be checked during erection |
| 10.4.3(c) | Foundations are sized for internal forces amplified by the factor D | The foundation is not considered apart from the panel force |
| 10.4.3(d) | Horizontal bridging at most h/2 apart in the studs of lateral load-resisting panels | Bridging is not skipped because there is a strap |
Which clauses apply to anchors?
Item (c) of 10.3 requires shear anchors, and foundation and storey connection anchors, to be designed to resist the base shear, the storey shear and the overturning moment. Clause 10.3.1.5 requires a hold-down at the chord studs of every load-bearing panel segment, and at least one in the shared chord stud where a sheathed and a braced panel sit side by side. Clauses 10.3.4.5 and 10.3.4.6 tie anchors to TS EN ISO 898-1 and to the shear force to be transferred.
Read nextWhat is the difference between a hold-down and a shear anchor?What does it say about floors?
Clause 10.5 requires floors to be calculated so that they transfer forces in their own plane safely to the panels. There are five conditions: applying the factor D, showing the force transfer by calculation, collectors where needed, no separate calculation for openings not exceeding 3%, and a joist bearing of at least 40 mm.
Read nextFloor and roof diaphragms: who delivers the load to the braced wall?What do the annexes cover?
- Annex 10A: Position and size rules for holes in profiles.
- Annex 10B: Alternative strength calculations for self-drilling screws and bolts.
- Annex 10C: Panel test principles; the average of at least three tests, a height/width ratio of 2/1, and the Equal Energy Elastic-Plastic rule.
Annex 10C shows how to determine strength for materials not in Table 10.5. So instead of matching a panel to a table value because it is "similar", you turn to testing if the conditions the text asks for are not met.
How does QSteelCAD relate to these clauses?
QSteelCAD does not calculate these clauses. It builds the panel, brace and bridging as producible geometry and prepares the production file. Whether the section, brace type and layout comply with the regulation is the project engineer's assessment.
Frequently asked
Which chapter of TBDY 2018 covers light steel?
Chapter 10: Special Rules for the Design of Light Steel Building Structural Systems under Earthquake Effects.
What ductility level does a braced panel system have?
According to 10.2.1.2, buildings whose earthquake effects are resisted entirely by braced panels are taken as a Limited Ductility Level system.
What is the T·e moment?
When the strap is on one face of the panel, the strap force T acts at a distance e from the stud axis. This product creates an additional moment in the stud and enters the stud calculation under 10.4.3(a).
How far apart should horizontal bridging be?
Clause 10.4.3(d) asks for at most h/2 spacing in the studs of lateral load-resisting panels, where h is the panel height.
This article is general information. It does not replace project calculations, an engineer's approval or the official text. Articles and values were read from the texts in force on the article's date.
