| Report # | 113 |
| Report Date | 01-10-2005 |
| Country | ITALY |
| Housing Type | Stone Masonry House |
| Housing Sub-Type | Stone Masonry House : Rubble stone without/with mud/lime/cement mortar |
|
Author(s)
|
Mauro Sassu, Chiara Cei |
|
Reviewer(s)
|
Svetlana N. Brzev |
Important
This encyclopedia contains information contributed by various earthquake engineering professionals around the world. All opinions, findings, conclusions & recommendations expressed herein are those of the various participants, and do not necessarily reflect the views of the Earthquake Engineering Research Institute, the International Association for Earthquake Engineering, the Engineering Information Foundation, John A. Martin & Associates, Inc. or the participants' organizations.
Summary
This construction originated during the Middle Ages in response to the threat of military invasions. The building plan is a square lattice, 5-7 meters, formed by three or four floors, with one room on each floor, and a total height of 15-20 m. It is a common technique found in Pisa but also found frequently in many municipalities of Tuscany and adjacent districts. The structure of the building is supported by four stone columns connected by arches (circle or ogival) or by beams at each floor; the floor is supported by a series of wood beams (especially pine) with wood tables and/or clay blocks. The upper floors of the earlier historic buildings often contained a wood balcony supported by cantilevered wood beams. Some balconies were fully enclosed structures with clay-tile roofing. The entrance on the first floor could be accessed by means of a detachable wood staircase.
1. General Information
Buildings of this construction type can be found in Mainly in Tuscany, but some of these buildings are also found in surrounding regions. This type of housing construction is commonly found in urban areas. This construction type has been in practice for more than 200 years ago.
Currently, this type of construction is not being practiced. The Casa Torre type originated around 1100 AD and was modified during the 17th century by incorporating the single masonry towers into adjacent buildings.
Figure 1: "Il Campano."
| 
Figure 2: Typical early version of tower: very slender structure with stone pillars. | 
Figure 3: Axonometry of the original version of the tower in Figure 2. |
Figure 4: "Torre della Verga d'oro" (Gold bar): structural arrangement of the original version. | 
Figure 5: Tower of "S. Pietro in Vicoli" (11th-12th century); subsequently it was converted into a bell tower. | 
Figure 6: Axonometry of the tower of "S. Pietro in Vicoli." |
Figure 7: Example of modified position of openings in the fa | 
Figure 8: East tower of S. Martino alla Pietra (beginning of 12th century). It has been incorporated into adjacent buildings.
Structural deficiencies have been caused by the subsequent unaligned openings as well as by the wide doorways at the ground-flo | 
Figure 9: "Il Campano" (bell tower): detail of the holes (black circle) made to support the framework (while the tower was being built) and the balcony after it was finished. The balconies were also strengthened by wood beams supported by shaped stones (r |
Figure 10: Typical section of the building.
| 
Figure 11: Design plan with the arrangement of steel reinforcement bars. | 
Figure 12: Opposite walls are connected by the use of tie-rods, with evident improvement in seismic behavior. |
Figure 13: "Torre della Verga d'oro."
Structural reinforcements: two large arched openings supporting horizontal forces at the base of the tower have been infilled by clay units. |
2. Architectural Aspects2.1 Siting
These buildings are typically found in flat terrain. They do no have common walls with adjacent buildings. The typical plan dimensions of the Casa Torre were 6 meters; sometimes adjacent buildings were created with two common pillars When separated from adjacent buildings, the typical distance from a neighboring building is 6 meters.
2.2 Building Configuration
Three or four floors; one room over each other, in an approximately square plan. In the first version (ca 1100), the openings were situated on one, or perhaps two, opposite walls. In the second period (ca 1200), openings might be seen on all four walls. In most cases, the openings were centered, vertically aligned, and narrow (0.80-1.20 m) in relation to the total dimension of the wall (6 m). Originally, the ground floor contained no openings (the entrance was accessed on the first floor with the help of a ladder); afterwards, wider openings (1.5-2.5 m) were created, mostly at the ground-floor level.
2.3 Functional Planning
The main function of this building typology is single-family house. The height of the house was indicative of the family's prestige, so rich families competed to attain the greatest height. In a typical building of this type, there are no elevators and 1-2 fire-protected exit staircases. None.
2.4 Modification to Building
Incorporating single masonry towers with adjacent buildings was often undertaken to create a unique "Palazzo" with wider buildings or multifamily dwellings.
3. Structural Details3.1 Structural System
| Material | Type of Load-Bearing Structure | # | Subtypes | Most appropriate type |
| Masonry | Stone Masonry
Walls | 1 | Rubble stone (field stone) in mud/lime
mortar or without mortar (usually with
timber roof) | ☑ |
| 2 | Dressed stone masonry (in
lime/cement mortar) | ☐ |
| Adobe/ Earthen Walls | 3 | Mud walls | ☐ |
| 4 | Mud walls with horizontal wood elements | ☐ |
| 5 | Adobe block walls | ☐ |
| 6 | Rammed earth/Pise construction | ☐ |
Unreinforced masonry
walls | 7 | Brick masonry in mud/lime
mortar | ☐ |
| 8 | Brick masonry in mud/lime
mortar with vertical posts | ☐ |
| 9 | Brick masonry in lime/cement
mortar | ☐ |
| 10 | Concrete block masonry in
cement mortar | ☐ |
| Confined masonry | 11 | Clay brick/tile masonry, with
wooden posts and beams | ☐ |
| 12 | Clay brick masonry, with
concrete posts/tie columns
and beams | ☐ |
| 13 | Concrete blocks, tie columns
and beams | ☐ |
| Reinforced masonry | 14 | Stone masonry in cement
mortar | ☐ |
| 15 | Clay brick masonry in cement
mortar | ☐ |
| 16 | Concrete block masonry in
cement mortar | ☐ |
| Structural concrete | Moment resisting
frame | 17 | Flat slab structure | ☐ |
| 18 | Designed for gravity loads
only, with URM infill walls | ☐ |
| 19 | Designed for seismic effects,
with URM infill walls | ☐ |
| 20 | Designed for seismic effects,
with structural infill walls | ☐ |
| 21 | Dual system – Frame with
shear wall | ☐ |
| Structural wall | 22 | Moment frame with in-situ
shear walls | ☐ |
| 23 | Moment frame with precast
shear walls | ☐ |
| Precast concrete | 24 | Moment frame | ☐ |
| 25 | Prestressed moment frame
with shear walls | ☐ |
| 26 | Large panel precast walls | ☐ |
| 27 | Shear wall structure with
walls cast-in-situ | ☐ |
| 28 | Shear wall structure with
precast wall panel structure | ☐ |
| Steel | Moment-resisting
frame | 29 | With brick masonry partitions | ☐ |
| 30 | With cast in-situ concrete
walls | ☐ |
| 31 | With lightweight partitions | ☐ |
| Braced frame | 32 | Concentric connections in all
panels | ☐ |
| 33 | Eccentric connections in a
few panels | ☐ |
| Structural wall | 34 | Bolted plate | ☐ |
| 35 | Welded plate | ☐ |
| Timber | Load-bearing timber
frame | 36 | Thatch | ☐ |
| 37 | Walls with bamboo/reed mesh
and post (Wattle and Daub) | ☐ |
| 38 | Masonry with horizontal
beams/planks at intermediate
levels | ☐ |
| 39 | Post and beam frame (no
special connections) | ☐ |
| 40 | Wood frame (with special
connections) | ☐ |
| 41 | Stud-wall frame with
plywood/gypsum board
sheathing | ☐ |
| 42 | Wooden panel walls | ☐ |
| Other | Seismic protection systems | 43 | Building protected with base-isolation systems | ☐ |
| 44 | Building protected with
seismic dampers | ☐ |
| Hybrid systems | 45 | other (described below) | ☐ |
The historic Casa Torre performs its structural functions by means of high-quality stones, moment-resisting connections of the beams, and regular plan shape.
3.2 Gravity Load-Resisting System
The vertical load-resisting system is others (described below). Limestone masonry pillars infilled with clay or sandstone walls with openings supported by wood or brick lintels. The floor is supported by small wood beams (span 1.7 m: distance 25-30 cm) which rest on two or three primary wood beams (span 5 m: distance 1.7 m).
3.3 Lateral Load-Resisting System
The lateral load-resisting system is others (described below). The system consists of plane frames formed by stone pillars and wood beams or wood-masonry arches. The "moment-resisting" connections between pillars and beams or arches are generally well executed. The stones at the edges have high mechanical strength. There are no moment-resisting connections between the floors and the walls or arches.
3.4 Building Dimensions
The typical plan dimensions of these buildings are: lengths between 7 and 12 meters, and widths between 4 and 8 meters. The building has 4 to 7 storey(s). The typical span of the roofing/flooring system is 5 meters. The typical storey height in such buildings is 3 meters. The typical structural wall density is up to 10 %. 5 to 10 %.
3.5 Floor and Roof System
| Material | Description of floor/roof system | Most appropriate floor | Most appropriate roof |
| Masonry | Vaulted | ☐ | ☐ |
Composite system of concrete joists and
masonry panels | ☐ | ☐ |
| Structural concrete | Solid slabs (cast-in-place) | ☐ | ☐ |
| Waffle slabs (cast-in-place) | ☐ | ☐ |
| Flat slabs (cast-in-place) | ☐ | ☐ |
| Precast joist system | ☐ | ☐ |
| Hollow core slab (precast) | ☐ | ☐ |
| Solid slabs (precast) | ☐ | ☐ |
Beams and planks (precast) with concrete
topping (cast-in-situ) | ☐ | ☐ |
| Slabs (post-tensioned) | ☐ | ☐ |
| Steel | Composite steel deck with concrete slab
(cast-in-situ) | ☐ | ☐ |
| Timber | Rammed earth with ballast and concrete or
plaster finishing | ☐ | ☐ |
| Wood planks or beams with ballast and concrete or plaster finishing | ☐ | ☐ |
| Thatched roof supported on wood purlins | ☐ | ☐ |
| Wood shingle roof | ☐ | ☐ |
| Wood planks or beams that support clay tiles | ☐ | |
Wood planks or beams supporting natural
stones slates | ☐ | ☐ |
Wood planks or beams that support slate,
metal, asbestos-cement or plastic corrugated
sheets or tiles | ☐ | ☐ |
Wood plank, plywood or manufactured wood
panels on joists supported by beams or walls | ☑ | ☐ |
| Other | Described below | ☑ | ☑ |
The existing wood floor/roof structures are not considered to be a rigid diaphragm unless they are tied with diagonal ties and connected to the walls.
3.6 Foundation
| Type | Description | Most appropriate type |
| Shallow foundation | Wall or column embedded in
soil, without footing | ☐ |
Rubble stone, fieldstone
isolated footing | ☑ |
Rubble stone, fieldstone strip
footing | ☐ |
Reinforced-concrete isolated
footing | ☐ |
Reinforced-concrete strip
footing | ☐ |
| Mat foundation | ☐ |
| No foundation | ☐ |
| Deep foundation | Reinforced-concrete bearing
piles | ☐ |
Reinforced-concrete skin
friction piles | ☐ |
| Steel bearing piles | ☐ |
| Steel skin friction piles | ☐ |
| Wood piles | ☐ |
| Cast-in-place concrete piers | ☐ |
| Caissons | ☐ |
| Other | Described below | ☐ |
4. Socio-Economic Aspects4.1 Number of Housing Units and Inhabitants
Each building typically has less than 10 housing unit(s). 1 units in each building. The number of inhabitants in a building during the day or business hours is 5-10 persons. The number of inhabitants during the evening and night is 5-10 persons. The ground floor was often modified further for handicrafts or commercial activities.
4.2 Patterns of Occupancy
Houses of this type were occupied only by the owner-family.
4.3 Economic Level of Inhabitants
| Income class | Most appropriate type |
| a) very low-income class (very poor) | ☐ |
| b) low-income class (poor) | ☐ |
| c) middle-income class | ☑ |
| d) high-income class (rich) | ☑ |
| Ratio of housing unit price to annual income | Most appropriate type |
| 5:1 or worse | ☐ |
| 4:1 | ☐ |
| 3:1 | ☐ |
| 1:1 or better | ☑ |
What is a typical source of
financing for buildings of this
type? | Most appropriate type |
| Owner financed | ☑ |
| Personal savings | ☐ |
Informal network: friends and
relatives | ☐ |
Small lending institutions / micro-
finance institutions | ☐ |
| Commercial banks/mortgages | ☐ |
| Employers | ☐ |
| Investment pools | ☐ |
| Government-owned housing | ☐ |
| Combination (explain below) | ☐ |
| other (explain below) | ☐ |
In each housing unit, there are no bathroom(s) without toilet(s), 1 toilet(s) only and no bathroom(s) including toilet(s).
Originally, the latrine was located on the wood balcony; later, the bathroom and latrines were placed inside the building. .
4.4 Ownership
The type of ownership or occupancy is outright ownership.
Type of ownership or
occupancy? | Most appropriate type |
| Renting | ☐ |
| outright ownership | ☑ |
Ownership with debt (mortgage
or other) | ☐ |
| Individual ownership | ☐ |
Ownership by a group or pool of
persons | ☐ |
| Long-term lease | ☐ |
| other (explain below) | ☐ |
5. Seismic Vulnerability5.1 Structural and Architectural Features
Structural/
Architectural
Feature | Statement | Most appropriate type |
| True | False | N/A |
| Lateral load path | The structure contains a complete load path for seismic
force effects from any horizontal direction that serves
to transfer inertial forces from the building to the
foundation. | ☑ | ☐ | ☐ |
Building
Configuration | The building is regular with regards to both the plan
and the elevation. | ☑ | ☐ | ☐ |
| Roof construction | The roof diaphragm is considered to be rigid and it is
expected that the roof structure will maintain its
integrity, i.e. shape and form, during an earthquake of
intensity expected in this area. | ☐ | ☑ | ☐ |
| Floor construction | The floor diaphragm(s) are considered to be rigid and it
is expected that the floor structure(s) will maintain its
integrity during an earthquake of intensity expected in
this area. | ☐ | ☑ | ☐ |
Foundation
performance | There is no evidence of excessive foundation movement
(e.g. settlement) that would affect the integrity or
performance of the structure in an earthquake. | ☑ | ☐ | ☐ |
Wall and frame
structures-
redundancy | The number of lines of walls or frames in each principal
direction is greater than or equal to 2. | ☐ | ☑ | ☐ |
| Wall proportions | Height-to-thickness ratio of the shear walls at each floor level is:
Less than 25 (concrete walls);
Less than 30 (reinforced masonry walls);
Less than 13 (unreinforced masonry walls); | ☑ | ☐ | ☐ |
Foundation-wall
connection | Vertical load-bearing elements (columns, walls)
are attached to the foundations; concrete
columns and walls are doweled into the
foundation. | ☑ | ☐ | ☐ |
Wall-roof
connections | Exterior walls are anchored for out-of-plane seismic
effects at each diaphragm level with metal anchors or
straps | ☐ | ☑ | ☐ |
| Wall openings | The total width of door and window openings in a wall
is:
For brick masonry construction in cement mortar : less
than ½ of the distance between the adjacent cross
walls;
For adobe masonry, stone masonry and brick masonry
in mud mortar: less than 1/3 of the distance between
the adjacent cross
walls;
For precast concrete wall structures: less than 3/4 of
the length of a perimeter wall. | ☐ | ☑ | ☐ |
| Quality of building materials | Quality of building materials is considered to be
adequate per the requirements of national codes and
standards (an estimate). | ☑ | ☐ | ☐ |
| Quality of workmanship | Quality of workmanship (based on visual inspection of
few typical buildings) is considered to be good (per
local construction standards). | ☑ | ☐ | ☐ |
| Maintenance | Buildings of this type are generally well maintained and there
are no visible signs of deterioration of building
elements (concrete, steel, timber) | ☑ | ☐ | ☐ |
| Other | | ☑ | ☐ | ☐ |
5.2 Seismic Features
| Structural Element | Seismic Deficiency | Earthquake Resilient Features | Earthquake Damage Patterns |
| Wall | Originally, the walls were not tied by means of steel or wood ties.
The connection of the multileaf walls is partially ensured by the wood floor beams.
| Massive stone masonry cavity walls, filled with sand, clay units, and lime inserted between the stone pillars, capable of dissipating seismic energy | Cracking (not necessarily due to an earthquake) at the interface of the pillars and walls. |
| Frame (columns, beams) | The corner pillars are made of large and squared stones with thin joints filled with lime mortar, well connected to the beams: the moment-resisting connection between pillars and beams is not ductile. | | |
| Roof and floors | Made of simply supported wood beams and planks, so they do not provide an effective connection between two opposite walls. | Very lightweight and elastic structures. | None |
| Other | Steel tie-rods to ensure anchorage between opposite masonry walls in case of structural restoration. | | |
In spite of its slender shape, this building achieves an enviable seismic performance for two main reasons. First, materials are made of good quality and secondly, the pillars or walls are well constructed. Moreover, in the event of masonry damage caused by shaking, the structure can dissipate energy without substantially reducing its overall vertical loading strength.
5.3 Overall Seismic Vulnerability Rating
The overall rating of the seismic vulnerability of the housing type is C: MEDIUM (i.e., moderate seismic performance), the lower bound (i.e., the worst possible) is B: MEDIUM-HIGH (i.e., poor seismic performance), and the upper bound (i.e., the best possible) is D: MEDIUM-LOW (i.e., good seismic performance).
| Vulnerability | high | medium-high | medium | medium-low | low | very low |
| | very poor | poor | moderate | good | very good | excellent |
Vulnerability
Class | A | B | C | D | E | F |
| ☐ | ☐ | ☐ | ☐ | ☐ | ☐ |
5.4 History of Past Earthquakes
| Date | Epicenter, region | Magnitude | Max. Intensity |
| 1846 | | 6 | |
| 1984 | | 5 | |
| 1987 | | 4.5 | |
No visible effects on load-bearing structures from earthquakes.
6. Construction6.1 Building Materials
| Structural element | Building material | Characteristic strength | Mix proportions/dimensions | Comments |
| Walls | "Verrucano" or limestone masonry for blocks; lime mortar joints | 20 - 50 MPa (verrucano or limestone) compression strength; 1-4 MPa (mortar) compression strength. | | Big, regular-shaped blocks. The mortar layers are very thin and the gaps are not visible. |
| Foundation | "Verrucano" stone masonry support or clay units | 10-20 MPa (clay unit) compression strength 1-4 MPa (mortar) compression strength. | | |
| Frames (beams & columns) | Clay units masonry arches or wood beams. | 8-15 MPa (wood) collapse stress due to bending moment | | |
| Roof and floor(s) | Wood beams (chestwood and oak)
| 8-15 MPa (wood) collapse stress due to bending moment. | | |
6.2 Builder
The builder didn't live in this construction type. These buildings were made for rich and important families; the ordinary house is smaller and made of wood and clay units.
6.3 Construction Process, Problems and Phasing
In the first two floors, the walls consist of two parallel stone wythes filled with clay units and lime mortar joints. Both wythes are made of large, sharp, squared stones with thin layer of mortar without gaps. The upper floors are made of smaller stones approximately shaped with bigger mortar gaps; large squared stones are still used in the corners and overlap masonry units in order to have adequate connection to the perimeter walls. Roof and floor beams are supported by particular shaped stones coming out of the walls.The framework is supported by wood beams embedded in specific holes in the front, which are still visible (see picture). The construction of this type of housing takes place incrementally over time. Typically, the building is originally not designed for its final constructed size. As they became richer and more powerful, many owners increased the height of their "casa torre" in a competition with the neighboring families for greater status.
6.4 Design and Construction Expertise
Technical historical knowledge and devices were remarkable; several original buildings constructed in the 12th century are well preserved with almost no specific maintenance problems. These buildings didn't require knowledge of engineering or analytical design: the builder followed unwritten rules and knowledge based on experience and tradition.
6.5 Building Codes and Standards
This construction type is addressed by the codes/standards of the country. Title of the code or standard: D.M. (Ministerial Decree) 20 November 1987 (Italian Code on Masonry Structures) D.M. 16 January 1996 (Italian Seismic Code)
Year the first code/standard addressing this type of construction issued: 1974
National building code, material codes and seismic codes/standards: Replaced O.M. (Ministerial Order) 20 March 2003 n. 3274 with further modifications
When was the most recent code/standard addressing this construction type issued? A national seimic code was issued in several Tuscany zones in July 1981.
Building Code enforcement was not available. From 1088-1092, church regulations limited the height of the towers in order to prevent any one family from gaining too much power and control. Constructing wood galleries on the outside walls has been prohibited for safety reasons since 1300.
6.6 Building Permits and Development Control Rules
This type of construction is an informal, and not authorized as per development control rules. Building permits are not required to build this housing type.
6.7 Building Maintenance
Typically, the building of this housing type is maintained by Builder. These buildings are commonly listed by the local heritage conservation office. (Soprintendenza ai Beni Architettonici, Artistici e Storici).
6.8 Construction Economics
In modern times, construction of building improvements and retrofitting is particularly concerned about preserving the original features. The average refurbishment cost is about 1.000 euros/m2. Refurbishment of this building type is under the strict control of the Historic Superintendent; only skilled laborers --- a builder, one assistant, a minimum of two skilled laborers and two manual laborers --- are allowed to perform work on these buildings.
7. Insurance
Earthquake insurance for this construction type is typically not available. For seismically strengthened existing buildings or new buildings incorporating seismically resilient features, an insurance premium discount or more complete coverage is not available. Earthquake insurance is not available in Italy.
8. Strengthening
8.1 Description of Seismic Strengthening Provisions
Strengthening of Existing Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Transverse connection between opposite walls | Steel tendons: grid wood floor frame |
| Vertical settlement | Reinforcement of the foundations with RC tub-fix micropiles |
8.2 Seismic Strengthening Adopted
Has seismic strengthening described in the above table been performed in design and construction practice, and if so, to what extent?
Steel bars are used as connections between opposite walls or to absorb horizontal forces in the arched beams of several buildings.
Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake?
Sometimes the work has been done to repair structural damage or to stop potential cracking of the masonry (not necessarily after an earthquake); sometimes it's undertaken just to stabilize the building.
8.3 Construction and Performance of Seismic Strengthening
Was the construction inspected in the same manner as the new construction?
Inspections were not routinely performed.
Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineer involved?
The building was constructed by a contractor without the involvement of an engineer or architect.
What was the performance of retrofitted buildings of this type in subsequent earthquakes?
Generally remarkable, but highly dependent on the quality of the strengthening work; subsequent earthquakes have had no effect on load-bearing structures.
Reference(s)- Pisa com'era : archeologia, urbanistica e strutture materiali
Redi,R.
Sec.V-XIV, GISEM-LIGUORI EDITORE, Napoli 1991
- An extrados-only restoration technique for raising and reinforcing of brick folio vaults
Sassu,M.
5th International Conference on Restoration of Architectural Heritage - Firenze 2000, vol. 3, pp. 3.2-, Firenze 2000
Author(s)- Mauro Sassu
Associate Professor, Dept. of Structural Engineering, University of Pisa
Via Diotisalvi 2, Pisa 56126, ITALY
Email:m.sassu@ing.unipi.it FAX: 39 050 554597
- Chiara Cei
Engineer, D.I.S.
Viale Italia 255, Livorno , ITALY
Email:angiochi@sysnet.it
Reviewer(s)- Svetlana N. Brzev
Instructor
Civil and Structural Engineering Technology, British Columbia Institute of Technology
Burnaby BC V5G 3H2, CANADA
Email:sbrzev@bcit.ca FAX: (604) 432-8973
