Nickel-containing stainless steel rebar is increasingly being used to ensure that infrastructure such as bridges, overpasses, and tunnels can withstand the test of time, even in the harshest environments.

Stainless steel has been used in construction since its invention over a century ago. Stainless steel products offer aesthetic appeal, corrosion resistance, low maintenance requirements, and good strength, toughness, and fatigue properties. Stainless steel is easy to fabricate and is fully recyclable at the end of its service life. They are the preferred materials for applications in challenging environments, including industrial processing facilities, coastal areas, or structures exposed to de-icing salts. The high ductility of stainless steel is a useful property for resisting seismic loads.

Typical applications for austenitic and duplex stainless steels include:

Beams, columns, platforms, and supports in water treatment plants, pulp and paper manufacturing, nuclear, biomass, chemical, pharmaceutical, and food and beverage industries

Main beams and columns, pins, railings, balustrades, cable sheaths, and expansion joints in bridges

Sea walls, docks, and other coastal structures

Reinforcing bar in concrete structures

Curtain walls, roofing, canopies, tunnel linings

Support systems for curtain walls, masonry structures, tunnel linings, etc.

Safety barriers, handrails, street furniture

Fasteners and anchoring systems in timber, stone, masonry, or rock

Structural members and fasteners in swimming pool buildings (special precautions should be taken for structural members in swimming pool environments due to the risk of stress corrosion cracking)

Blast and impact-resistant structures such as security walls, gates, or bollards

Fire and blast walls, cable trays, and walkways on offshore platforms

Structural Applications

Introduction

Stainless steel is a highly versatile material with a unique set of properties that can be utilized in structural (load-bearing) applications.

Plate, section, bar, and tube products in austenitic and duplex stainless steel grades are widely available. A range of hot-rolled or welded structural sections (I-beams, angles, channels, tees, hollow sections) are stocked in standard austenitic materials. Duplex stainless steels are typically available by special order. Other structural sections can be produced by cold forming, extrusion, or laser fusion. A wide variety of stainless steel bolts, screws, and other types of fasteners are available.

Infrastructure

Structural applications of stainless steel in infrastructure include load-bearing members (girders, arches, ties, etc.) in pedestrian, highway, and railway bridges, as well as tunnels (lining support frames, maintenance walkways, lighting and sign supports). Stainless steel is also widely used in street furniture (guardrails, handrails) and subway station entrance structures.

Architecture

In commercial buildings and structural facades, stainless steel structural members are a popular choice for supporting glass curtain walls, as well as for canopies supports, balconies, and other applications where corrosion resistance and strength are required to reduce maintenance needs.

Stainless steel is an ideal material for fastening timber, stone, and masonry, anchoring systems, and support angles. These connections are often inaccessible or difficult to replace. Furthermore, wood and masonry are inherently corrosive to other metals and can absorb moisture and corrosive chemicals over time.

In swimming pools, stainless steel is used for both architectural and structural applications such as pool liners, handrails, ladders, structural members, fasteners, furniture, diving structures, decorative items, and water treatment and ventilation systems. However, due to the risk of stress corrosion cracking, special precautions are required for stainless steel structural members with high residual stresses in swimming pool environments.

Industrial Structures

Stainless steel is used in blast and impact-resistant structures such as blast and security walls, gates, security barriers, and bollards. This is because, due to its excellent ductility (especially austenitic grades) and strain hardening characteristics, it can absorb considerable impact without fracturing. This high ductility is a useful property required to resist seismic loads.

Stainless steel is increasingly used in industrial structures for the water treatment, pulp and paper, nuclear, biomass, chemical, pharmaceutical, and food and beverage industries. Industrial structural applications include platforms, guardrails/gates, and equipment supports.

Grade Selection

Grades Used in Structures

The vast majority of structural stainless steel applications utilize austenitic or duplex stainless steels.

Austenitic stainless steels offer an excellent combination of corrosion resistance, formability and fabricability with a design strength of around 220 MPa (32 ksi). They contain about 10% nickel. The basic chromium-nickel austenitic grade S30400/S30403 is suitable for rural, urban, and light industrial sites. The chromium-nickel-molybdenum austenitic grades S31600/31603 are higher alloyed grades that perform well in marine and industrial locations.

Duplex stainless steels, such as grade S32205, offer high strength of around 450 MPa (65 ksi), good wear resistance, and excellent resistance to stress corrosion cracking. It is called "duplex" because it has a two-phase microstructure consisting of ferritic and austenitic stainless steel grains, containing about 5% nickel.

In addition, newer lean duplex grades offer a combination of high strength with a lower alloyed chemical composition, making them less costly. Examples of lean duplex grades are S32101 and S32304. Nickel content is approximately 2-4%.

Ferritic stainless steels are occasionally used in structural applications, typically for thicknesses of 3 mm and under. They generally contain little or no nickel addition.

Material and Product Specifications

European and American standards that specify the chemical composition and mechanical properties of stainless steel flat and long products include:

EN 10088: Stainless steel – *Description of grades in EN 10088-4 for stainless steel flat products for construction*

ASTM A240/240M: Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications

ASTM A276: Standard Specification for Stainless Steel Bars and Shapes

Specifications for stainless steel bolts include:

EN ISO 3506: Mechanical properties of corrosion-resistant stainless steel fasteners

ASTM F593: Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs

ASTM A1082/1082M: Standard Specification for High-Strength Precipitation Hardening and Duplex Stainless Steel Bolting for Special

Purposes

Selecting the Right Grade

It is important that the selected stainless steel is suitable for the intended service environment, as cost generally increases with corrosion resistance.

A procedure for selecting the correct stainless steel grade for structural applications in different environments is found in Eurocode 3: Part 1.4 (EN 1993-1-4), the European design standard for structural stainless steel. Environmental severity is determined based on an assessment of the risk of exposure to chlorides (from seawater or de-icing salts) and sulfur dioxide. The cleanliness regime, including whether the structure is exposed to rainfall washing, is also considered. The selection procedure is fully explained with examples in the SCI Design Manual for Structural Stainless Steel (4th Edition) (published 2017).

Other important considerations include grade/product availability, surface finish requirements, and connection methods.

Performance of Stainless Steel in Structures

Stress-Strain Behavior

The stress-strain behavior of stainless steel differs from that of carbon steel. Carbon steel typically exhibits linear elastic behavior up to the yield stress, with a plateau before encountering strain hardening, whereas stainless steel has a more rounded response with no clearly defined yield stress. The yielding and work hardening characteristics of stainless steel mean that traditional carbon steel design rules do not apply. The "yield" strength of austenitic grades is approximately 200-240 MPa (29-35 ksi), and for duplex grades, it is 400-530 MPa (58-77 ksi).

The modulus of elasticity for stainless steel is very similar to that of carbon steel; a value of about 200×10³ N/mm² is commonly used for the types of stainless steel used in structural applications.

Stainless steel can absorb considerable impact without fracturing, thanks to its excellent ductility (especially austenitic grades) and strain hardening characteristics.

High Temperature Performance

The different composition of stainless steel means different thermal properties compared to carbon steel. Austenitic stainless steel has a coefficient of thermal expansion about 30% higher than carbon steel, while the value for duplex stainless steel is only about 10% higher. The thermal conductivity of austenitic and duplex stainless steels is about 30% that of carbon steel.

Austenitic stainless steels retain their strength better than carbon steel at temperatures above about 550ºC and retain their stiffness better at all temperatures. Consequently, a stainless steel column will maintain its load-carrying capacity longer than an equivalent carbon steel member.

Low Temperature Performance

Austenitic stainless steels are widely used for cryogenic service down to liquid helium temperatures (-269°C) because they do not exhibit a transition from ductile to brittle fracture even at such low temperatures.

Fatigue

The fatigue resistance of austenitic and duplex stainless steels is considered to be at least equivalent to that of carbon steel; hence, guidance for estimating structural fatigue strength applicable to carbon steel is used.

Sustainability

While the initial cost of stainless steel is higher than carbon steel, savings in corrosion protection coatings, reduced inspection frequency, maintenance, downtime, and replacement costs can far outweigh the higher initial material cost. The benefits of a long service life are particularly valuable for bridge structures, which are typically designed for a service life of 70-100 years.

Stainless steel is 100% recyclable and can be recycled indefinitely into new high-quality stainless steel.

Design, Fabrication, and Installation

Structural Design

The yielding and work hardening characteristics of stainless steel mean that traditional carbon steel design rules based on observed limits of elastic deformation are not all applicable. Different design rules are required for beams and columns susceptible to local or global buckling. Deflections for heavily loaded beams will be greater than for an equivalent carbon steel beam.