The Design of Bolted Connections According to Standards
By Jorge Santiago Chau Chau
Students often experience confusion when analyzing bolted connections,
particularly when distinguishing between design criteria and calculation methods. To
clarify the proper use of standards in this field, the following summary is presented.
1. Introduction
Bolted connections are a type of temporary joint that allow components to be
assembled and disassembled without compromising their physical integrity or
mechanical properties. Their use is widespread in mechanical and structural
engineering due to advantages such as:
•
•
•
Ease of assembly and disassembly.
Compatibility with different materials.
Absence of thermal distortions, unlike welding.
2. Classification by Purpose
Bolted connections can be classified according to their application, and each type is
governed by specific standards that define design, manufacturing, and installation
requirements:
•
•
•
Mechanical component connections
Used in machinery and transmissions subjected to combined stresses and
cyclic loads. Design must account for fatigue and loosening due to
vibration.
o Reference standards: ISO 898 and DIN standards, which regulate
mechanical properties and bolt dimensions.
Sealing and hermetic connections
Applied in pressure vessels and piping systems, where the priority is to
ensure tightness. These connections often incorporate gaskets or special
washers to prevent leakage under pressure and temperature conditions.
o Reference standards: ASME Boiler and Pressure Vessel Code
(BPVC) and ASME B16 (flanges and fittings).
Structural connections in large-scale construction
Used in bridges, buildings, and steel structures, where bolts must withstand
significant static and dynamic loads. Design considers shear and tensile
resistance, as well as safety against seismic and wind loads.
o Reference standards: AISC (American Institute of Steel
Construction), with design methods LRFD (Load and Resistance
Factor Design) and ASD (Allowable Stress Design).
3. Calculation Methods and Main Stresses
The design of bolted connections is based on classical strength of materials theory,
applied through formulas such as:
These formulas are universal, but each standard introduces different safety factors,
load coefficients, and installation requirements, tailored to the risks of each
application.
4. Differences Among Standards
Although all standards are based on the same mechanical theories, they differ in:
•
•
•
•
Safety factors: higher in ASME due to leakage risks, moderate in DIN/ISO for
machinery, and adjusted in AISC-LRFD for extreme loads.
Bolt classification: DIN/ISO uses strength classes (8.8, 10.9, 12.9);
ASTM/AISC uses grades (A325, A490); ASME certifies materials for pressure
and temperature.
Calculation methods: DIN/ISO applies direct formulas; ASME adds
hermeticity verification; AISC applies both LRFD and ASD.
Installation requirements: ASME requires pressure testing, AISC regulates
tightening torque and slip resistance, DIN/ISO specifies tolerances and
recommended torque values.
5. LRFD and ASD Methods in Structural Design
In structural engineering, AISC standards recognize two design approaches:
•
ASD (Allowable Stress Design)
o Compares calculated stresses with allowable stresses, obtained by
dividing material strength by a global safety factor.
o Historically dominant in structural design and still applied in mechanical
elements where direct stress control is practical.
o Its main advantage is simplicity and continuity with traditional
calculation methods.
•
LRFD (Load and Resistance Factor Design)
o Uses load factors ((\gamma)) and resistance factors ((\phi)) derived
from statistical and probabilistic models of variability in materials,
loads, and service conditions.
o Provides greater reliability in structures subjected to extreme loads
(seismic, wind, impact).
o Beyond reliability, LRFD enables economic optimization, as it adjusts
factors according to load type, reducing material usage without
compromising safety.
It is essential to emphasize that LRFD factors are specific to structural
applications and cannot be extended to other fields such as machinery or
pressure vessels. In those cases, ASD or standards like DIN/ISO and ASME must be
applied, as they address different risks such as fatigue, vibration, or hermeticity.
6. Conclusion
Bolted connections are fundamental in mechanical and structural engineering, but
their design depends on the regulatory context:
•
•
•
•
DIN/ISO → machinery and dimensional precision.
ASME → pressure safety and hermeticity.
AISC-ASD → traditional stress-based design, applicable in mechanics and
structures.
AISC-LRFD → statistical reliability and economic optimization in large-scale
structures.
Although all standards are based on the same strength of materials theories, what
differentiates them is how safety factors and acceptance criteria are applied,
adapted to the risks of each application.
References
•
•
•
•
Deutsches Institut für Normung. (2018). UNE-EN 15048-1:2018 Structural
bolted connections without preloading. Part 1: General requirements. Berlin:
DIN. Retrieved from https://www.une.org/encuentra-tu-norma/busca-tunorma/norma?c=N0059863
IngeMecánica. (n.d.). Calculation of bolted connections. Tutorial No. 32.
Retrieved from https://ingemecanica.com/tutorialsemanal/tutorialn32.html
Universitat Politècnica de Catalunya. (n.d.). Bolted connections. Lecture notes
on
steel
structures.
Retrieved
from
https://upcommons.upc.edu/bitstreams/13c582a4-83d6-46db-81ab48b64f310361/download
American Society of Mechanical Engineers. (2025). ASME B16: Flanges,
types,
and
pressure
ratings.
Retrieved
from
https://www.alibre.com/es/blog/asme-b16-flanges-types-standardsdimensions-pressure-ratings/
•
•
•
•
Tuberías de Acero. (n.d.). Reference tables for flange bolts according to ASME
B16. Retrieved from https://www.tuberiasdeacero.com/pdf/tienda/ZD6.pdf
American Institute of Steel Construction. (2005). Design of bolted connections:
LRFD
and
ASD.
Retrieved
from
https://studylib.net/doc/27422624/conexiones-atornilladas
American Institute of Steel Construction. (2025). AISC 360: Specification for
Structural
Steel
Buildings.
Retrieved
from
https://www.aisc.org/aisc/publications/current-standards/aisc-360/
Velasco González, J. de J. (n.d.). Steel structural design: AISC LRFD vs ASD
methodologies. Retrieved from https://studylib.es/doc/8982914/lrfd-vs-asd