Documento Básico SE-F (DB-SE-F) – Structural Safety: Masonry
The Documento Básico SE-F (DB-SE-F) constitutes the technical framework for the structural safety of masonry within the Código Técnico de la Edificación (CTE) in Spain. Issued by the Ministerio de Fomento, this regulatory document establishes the criteria and procedures for the structural verification of walls made of small units—such as brick, concrete blocks, aerated concrete, and stone—bonded with mortar. The current text incorporates modifications from Real Decreto 732/2019 and sits under the broader framework of Real Decreto 314/2006, which approved the Spanish Technical Building Code.
The scope of this regulation covers load-bearing walls, arriostramiento walls, and supported masonry elements. It governs structural design, durability through exposure classes, material specifications for units and mortars, and execution control categories. Specific project documentation requirements are detailed, including technical specifications for masonry elements in memories and plans. The document excludes dry-stack masonry, masonry without tie-beams (encadenados), and irregular stone walls where thickness is achieved via amorphous fillings between ashlar faces.
This reference document provides the mechanical parameters and safety factors necessary for professional structural analysis. It includes technical tables for movement joint spacing, exposure classes, and material resistance values essential for architects and structural engineers.
Calculation Bases and Movement Joints
Structural analysis is based on state-of-the-art limit states, allowing for a rigid-plastic stress-strain diagram in wall behavior analysis. A primary requirement involves the provision of movement joints to accommodate thermal and moisture expansion, creep, and shrinkage.
- Maximum Joint Spacing: For sustained natural stone masonry, the maximum distance is 30 meters. For ordinary concrete units, it is 20 meters, while for autoclaved aerated concrete, it is 22 meters.
- Ceramic Brick Variables: Joint distances for ceramic brick vary between 8 meters and 30 meters depending on the final mortar shrinkage and piece moisture expansion.
- Prestressing Factors: The partial safety factor for prestressing actions after losses is established at 1.00 for ultimate limit state checks.
Durability and Exposure Classes
The regulation categorizes environments into general and specific exposure classes to define the chemical and physical aggressiveness to which the masonry will be subjected during its service life.
- General Classes: Includes Class I (Non-aggressive interior), Class IIa/IIb (Medium/High humidity exterior), and Class IIIa/IIIb/IIIc (Marine environments).
- Specific Classes: Covers chemical aggression (Qa, Qb, Qc), freezing with or without de-icing salts (H, F), and erosion (E).
- Reinforcement Protection: Minimum mortar cover for reinforcements is 15 mm for galvanized steel or stainless steel in aggressive environments. Bed-joint reinforcement in Class I may use unprotected carbon steel, but Classes IIa and IIb require galvanized protection with at least 900 g/m² of zinc.
Material Classification and Strength
Masonry units are grouped based on hole volume and shell thickness, which determines the formulas applied for characteristic compression resistance.
- Unit Groups: Table 4.1 defines groups as Maciza (Solid, ≤25% holes), Perforada (Perforated, ≤45-50% holes), Aligerada (Lightweight, ≤60% holes), and Hueca (Hollow, ≤70% holes).
- Mortar Grades: Ordinary mortars are designated as M1 to M20 based on compression strength in N/mm². Mortar strength must not exceed 0.75 of the normalized piece resistance to prevent brittle failure.
- Minimum Normalized Strength: The standard minimum strength for units (fb) is 5 N/mm², though lower values are permitted for non-load-bearing walls under specific stress limitations.
Structural Verification of Walls
The document details procedures for verifying walls under vertical loads, shear, and local lateral actions. It introduces the reduction factor Φ to account for slenderness and eccentricity.
- Minimum Thickness: All load-bearing walls must maintain a minimum thickness of 115 mm.
- Slenderness Limit: The geometric slenderness ratio (hd/td) must not exceed 27.
- Shear Resistance: Defined as the sum of the masonry's own shear strength and the contribution of any bed-joint reinforcement, capped at 2.0 N/mm² multiplied by the compressed length and thickness.
Execution Categories and Control
The partial safety factors applied in calculations depend on the execution category (A, B, or C) and the level of manufacturing control (I or II).
- Category A: Requires certified units and mortars, certified laboratory tests of the masonry, and daily constructor supervision.
- Tolerances: Verticality deviation (desplome) is limited to 20 mm per floor height and 50 mm for the total building height.
- Maintenance: Masonry with bed-joint reinforcement must be inspected at least every 10 years to verify the efficacy of protective finishes.
Frequently Asked Questions
What is the minimum thickness for a load-bearing masonry wall in Spain?
According to Section 5.2.1 of DB-SE-F, every load-bearing wall must have a thickness of at least 115 mm.
What are the maximum distances between movement joints for brick walls?
The distance varies based on material properties; for ceramic brick, the maximum spacing ranges from 8 to 30 meters, depending on moisture expansion and mortar shrinkage values.
Which mortar grade is required for reinforced masonry?
Section 4.2 specifies that ordinary mortar for reinforced or prestressed masonry must not be lower than grade M4.
How is the slenderness of a masonry wall limited?
The geometric slenderness ratio, defined as the calculation height divided by the calculation thickness (hd/td), must not exceed 27.
What is the minimum support length for concentrated loads on masonry?
The support length of a concentrated load on a wall must not be less than 100 mm.
How often must reinforced masonry with self-protection be reviewed?
Masonry containing bed-joint reinforcement with self-protection treatments must be inspected at least every 10 years.
What is the minimum mortar cover for galvanized reinforcement?
The minimum mortar cover relative to the exterior edge must not be less than 15 mm.
What are the execution categories defined in DB-SE-F?
The document defines three categories: A (highest control with certified materials and daily inspection), B (standard control), and C (reduced control).
