72789 - Structural Strengthening & Rehabilitation

Learning outcomes

The course Structural Strengthening and Rehabilitation aims to give students a real structural design ability in many different areas through many different techniques. The course focuses on all materials present in existing structures like masonry, concrete, steel and timber. It includes various information and annotations on non-destructive testing of materials and evaluation of damage levels in historic structures, presenting them in the framework of Mohr-Coulomb materials. The strengthening and rehabilitation design is developed by using traditional and innovative techniques. Among them, the case of restoration with fibre-reinforced polymers is discussed in detail, presenting both the theoretical basis and the design rules, with applications to many important examples. The course discusses several relevant cases of structural damage in detail: soil settlement, earthquake, fire, corrosion, and shock. Some cases of problem solutions are discussed in detail, by comparing the different strengthening techniques. The analysis is mainly worked out with hand calculation so that students can widen their design capacity by applying themselves to some homework proposed at the end of the course, without the need for complex structural analysis programs. The course is expected to form students for real professional strengthening activities, giving them the ability to investigate the damage severity and select the most appropriate strengthening technique.

Course contents

The course focuses on understanding the mechanisms underlying the damages and defects that we detect on structures, and on the restoration techniques available in the designer’s toolbox.

The lectures involve a detailed analysis of the possible degradation phenomena occurring in concrete, masonry, steel and timber structures, such as cracking, corrosion, ageing, chemical or biological attack. It will cover even special situations such as fire or seismic damage.

Many experimental techniques, which can point out material properties relevant for design, will be presented. Cases of buildings with insufficient design capacity will be discussed in the light of forensic engineering.

The theoretical basis of different strengthening techniques will be detailed with many examples of application to real situations, comparing the efficiency of the different solutions.

In particular, solutions based on composite materials will be explored in several directions:

• Strengthening of masonry structures with steel, fibre reinforced polymers (FRP), or fibre reinforced mortars (FRM),
• Strengthening of concrete structures with additions, steel caging or FRP networks,
• Strengthening of timber structures with timber, steel or concrete additions,
• Strengthening of foundations with slabs, injections, and piles.

The design of the strengthening systems will be supported with pervasive theoretical instruments such as Mohr-Coulomb materials, fracture mechanics, limit analysis, and technical composite beam theory.

The student at the end of the course will easily manage a deep knowledge of the different structural degradation mechanisms and a wide set of strengthening techniques, each one with its design rules and standard requirements in terms of safety evaluation.

Readings/Bibliography

PAPERS DEALING WITH SPECIFIC STRUCTURAL STRENGTHENING THEMES:

Tarozzi, M., Pignagnoli, G. & Benedetti, A. (2022), Evaluation of the residual carrying capacity of a large-scale model bridge through frequency shifts. J Civil Struct Health Monit.

Benedetti, A., Tarozzi, M. (2022) Compressive strength of heterogeneous masonry walls containing blends of brick types. Materials and Structures, 55(71).

A. Benedetti, M. Tarozzi and L. Benedetti, (2021), Combined Shear-Flexural Verification of in Plane Loaded Reinforced and Unreinforced Masonry Walls, Proc. of the SAHC Conference 2021.

Tarozzi M., Pignagnoli G., Benedetti A., (2020), Identification of damage-induced frequency decay on a large-scale model bridge, Engineering Structures, 221, 111039, ISSN 0141-0296.

Benedetti A., Tarozzi M., (2020), Interpretation formulas for in situ characterization of mortar strength, Construction and Building Materials, 242, 118093, ISSN 0950-0618.

Benedetti A., Tarozzi M., (2019), Toward a quantitative evaluation of timber strength through on-site tests, In: Advances in Engineering Materials, Structures and Systems, CRC Press.

Benedetti A. (2019) In Plane Behaviour of Masonry Walls Reinforced with Mortar Coatings and Fibre Meshes, International Journal of Architectural Heritage, 13:7, 1029-1041.

Benedetti, A. (2019). Diagonal Compression Behaviour of Masonry Walls Reinforced with FRM Coatings. In: Structural Analysis of Historical Constructions, RILEM Bookseries vol 18. Springer.

Benedetti, A., Pignagnoli, G. & Tarozzi, M. (2018), Damage identification of cracked reinforced concrete beams through frequency shift. Materials and Structures 51, 147.

Marastoni D., Pelà L., Benedetti A., Roca P., (2016), “Combining Brazilian tests on masonry cores and double punch tests for the mechanical characterization of historical mortars”, Construction and Building Materials, 112, pp. 112-127, ISSN 0950-0618.

Pelà L., Benedetti A., Aprile A., Mangoni E. (2013), ”Seismic Assessment Of The Milano Centrale Railway Station”, International Journal of Architectural Heritage. 7, pp. 609-627, ISSN:1558-3058

Pelà L., Aprile A., Benedetti A. (2012), “Experimental Study of Retrofit Solutions For Damaged Concrete Bridge Slabs”, Composites Part B: Engineering. 43-5, pp. 2471-2479, ISSN:1359-8368

Benedetti A., (2003), “Approximate Optimal Design Of Fire-Resisting Beams And Columns”, Journal of Constructional Steel Research, 59-10 pp. 1251-1266

Benedetti A., (1998), "On The Ultrasonic Pulse Propagation Into Fire Damaged Concrete", ACI Structural Jour., 95-3.

NORMS:

EN 1992:1-2, Eurocode 2: Design of concrete structures - Part 1-2: General rules - Structural fire design

EN 1993:1-2, Eurocode 3: Design of steel structures - Part 1-2: General rules -Structural fire design

EN 1995:1-2, Eurocode 5: Design of timber structures - Part 1-2: General -Structural fire design

EN 1998:3, Eurocode 8: Design of structures for earthquake resistance - Part 3: Assessment and retrofitting of buildings

CNR-DT 200 R2/2025: Guidelines for the Design, Execution, and Inspection of Structural Strengthening Interventions Using Fiber-Reinforced Composites

Teaching methods

The course will be developed with in-person lectures based on the presentation of slides, the use of hand calculations on the blackboard, discussion with the audience, and specimen distributions of the composite materials involved in the presented interventions.

All the course slides are collected in the “VIRTUALE” site, so that they can be freely distributed to the students.

The students are requested to carry out on their own some exemplary calculations as homework. This helps in practising with decisions due in design works and better understand the safety evaluation rules given by the norms.

Assessment methods

The students are requested to ask for an appointment after the end of the course for an exam evaluation. At the exam, they will present the completed homework and discuss the theoretical background of the designed strengthening works.

The appointment is granted all along the year with a mean delay of one week. In case of not passing the exam, the student can ask for a new appointment after a month.

The evaluation of the student preparation is mainly based on the demonstration that the student has design ability and understands the theoretical bases of used design rules used. Evidence of more than 40 years of exams demonstrates that it is sufficiently easy to obtain an average mark, although only very few students exercise themselves up to a sound design knowledge, worthy of the higher mark. However, I am still looking at having many of those enthusiastic future designers!

Teaching tools

All the course material and many other papers are collected in the VIRTUALE site, and freely downloadable for students.

For the design work, you need only the hand calculator, but you can still use any digital and computer resource that you retain helpful in your effort.

Office hours

See the website of Andrea Benedetti