Seismic Retrofitting of Historic And Heritage Buildings

Historic structures are valuable regional cultural assets that should be preserved. They can occasionally serve as a potential source of funding and a catalyst for the neighborhood’s economic revival. Of course, not every old building qualifies as historic or monumental because the criteria used to determine whether a structure is historic might vary among cultures and nations.

A building is considered historic in the United States if it is at least 50 years old, listed on or possibly qualified for the National Register of Historic Places, as well as other state or local registers, as an individual structure, or as a component structure in a neighborhood. Unless they can be deemed historic, older buildings are typically demolished and replaced by newer ones for economical and performance reasons.

Retrofitting Process of Historic And Heritage Buildings

The phrase “retrofit process” refers to a broad range of interventions, including preservation, rehabilitation, restoration, and reconstruction. The process of putting measures in place to preserve a historic property’s original shape, integrity, and materials is known as preservation.

The term “rehabilitation” describes the act of giving a property new use through repairs, additions, and renovations while retaining the qualities that communicate its historical importance. The practice of accurately restoring a structure to how it appeared at a specific time is known as restoration.

Replicating a property at a particular moment is referred to as reconstruction. In the retrofit process, choosing the proper treatment technique is a difficult decision that must be made specifically for each project.

Depending on the project’s goals, the preservation and renovation of historic buildings may involve a wide range of different technical factors, including structural performance under earthquake and wind loads, geotechnical hazards and solutions, weathering and water infiltration, fire life safety, and more.

The structural renovation or retrofit of these buildings presents many technical challenges to A/E design professionals because the design methodology, building materials, and construction techniques used in their initial construction were frequently significantly different from those used in contemporary buildings.

Materials Development in Building Construction

Building materials have changed steadily throughout the course of history, and over the past century, the rate of change has increased. Some of the primary reasons for the differences between traditional and modern building materials are developments in material engineering and metallurgy, the development of plastics and fiber-reinforced composites, and changes in the manufacture and handling of existing building materials. Improvements to traditional building materials that are employed in both old and modern structures include:

Buildings Made of Masonry, Stone, And Adobe

Up until the latter part of the eighteenth century, bearing wall buildings predominated; however, steel frame skeletons have since taken over as the standard structural form for major buildings. Masonry buildings are restricted to specific building types and distinct places in modern development.

While adobe or bricks have slightly grown into stronger, more resilient building materials with standardized shapes and sizes, natural stone has not changed. By using stronger mortar and reinforcements to give better resilience and continuity, design and construction methods for masonry buildings are improved. The use of concrete-filled blocks is another significant advancement in masonry structure construction.

Timber and wood

Although wood hasn’t seen any significant change as a natural building material, modern technology offers strength grading techniques, wooden panel products, preservation treatment procedures, and wood protection.

Concrete

Over the course of the 20th century, concrete underwent substantial change. Concretes that were stronger and more durable were produced using improved ingredients, quality control, preparation, and casting techniques. Lightweight, highly workable, shrinkage-compensating, low-porosity, and fiber-reinforced concrete kinds are now possible thanks to advancements in concrete technology, the use of additives and plasticizers, and improved cements.

Hot-rolled reinforcing steel

Regarding the physical characteristics and shape, reinforcing steel has undergone significant development. The new ribbed reinforcement bars with low carbon content offer more ductility and a stronger link between the steel reinforcement and concrete than the original square cross-section, high carbon content, and smooth surface reinforcement bars.

Structural Steel

Within the last century, structural steel’s overall strength has increased. A number of steel shapes are now deemed obsolete and are no longer produced due to changes in section size and steel form attributes. In the process of designing a retrofit, differences in strength, ductility, and weldability must be taken into account.

Design Codes

Building codes have been changed frequently in recent years based on various lessons learnt from failures (especially earthquake related failures). The method we perform structural analysis and modeling has significantly altered thanks to advances in computer technology and software design.

In general, more recent regulations tend to mandate better continuity for seismic loads, increase structural system redundancy, and take advantage of inelastic structural capacity to absorb and dissipate earthquake stresses.

Challenges Encountered in Retrofitting Historic and Heritage Buildings

Common concerns in most retrofit projects include minimizing noise, disruption, and damage to neighboring structures as well as providing temporary shoring and support. Depending on the extent of damage, cost implications, historical value of the building, assessed risk and some other factors, the preferable retrofitting options are evaluated and selected to maintain the originality of old structures and reduce removal of architectural material from the building:

No Penetration of Building Envelope

The historic fabrication is left undisturbed because the technique doesn’t include any damaging procedure. Since structural elements are frequently either incorporated in or hidden by the finishing, this strategy is only really appropriate in a very small number of situations.

Penetration Without Breakage

The accessible structural component being retrofitted just needs a few holes to be drilled, such as micro piles, and epoxy injected.

Breakage With Repair

Many times, it is necessary to execute some damaging processes in order to gain access to the structural component or to carry out a retrofit process, such as upgrading welded connections or installing base-isolators.

Replace

Components are replaced when structural components cannot be modified to satisfy retrofitting aims or when the damage or deterioration cannot be rectified. Maintaining continuity, isolating the component, and providing support to the rest of the facility are all important considerations during the replacement process.

Rebuild

When a workable retrofitting option cannot be identified, the historic structure is either completely or substantially rebuilt. The cost of this alternative is higher, and the cultural and historical values may be impacted by the loss of authenticity. Usually, when a historic building needs to be renovated, new structural members are needed.

In order to preserve the historic fabric of the building, the new structural members must be concealed or exposed as if they were relatively recent additions to the building. Since these kind of modifications can be undone in the future without affecting the building’s historic fabric, it is frequently preferred to expose new structural elements.

Modern Techniques For Retrofitting Historic And Heritage Buildings

Numerous retrofitting alternatives exist now thanks to modern equipment and materials, which can be used to reduce seismic risk or enhance structural system performance. The following is a list of some of the most popular retrofitting techniques:

Post Tensioning

For buildings made of reinforced concrete or masonry, post tensioning is seen to be one of the most effective retrofit choices since it adds strength and ductility to the entire structure with little to no disruption. Masonry has a modest tensile strength and a comparatively high compressive strength.

As a result, hauling gravity-based loads is where it excels. However, significant levels of tensile stress are also produced by in-plane shear and out-of-plane lateral stresses. Typically, these induced tensile stresses are greater than the compressive stresses, necessitating the addition of reinforcement (often in the form of steel elements) to provide the structure the required strength and ductility.

Post-tensioning the reinforcing steel can dramatically increase the degree of compressive stresses while preventing more brittle tensile failures. Basically, a high-strength steel rod is inserted through a core hole that is made in the masonry wall. The foundation serves as the rod’s anchor point at the bottom. The rod is then subjected to intense tensile forces using a jack at the top of the wall.

Base Isolation

Base isolation will significantly reduce architectural and structural damage in the occurrence of a big earthquake by altering the structure’s natural period, which is utilized to dissociate the building’s response from seismic activity. The two primary types of isolation devices that have been used are sliders and elastomeric bearings.

Composite Wraps

Masonry components and reinforced concrete can be made more ductile and stronger without requiring any penetration by using composite wraps or carbon fiber jackets. Composite wraps, which add extra confinement, are most successful when applied to reinforced concrete columns (both circular and rectangular shapes).

Micro Piles

To increase the ultimate capacity of the foundation and decrease foundation deflection, micro-piles are used in seismic retrofitting and foundation rehabilitation projects.

Epoxy

One of the most adaptable materials for structural repair and modernization is epoxy, which can be employed as a sealer, glue, or mortar. Epoxy is frequently used to bind reinforcement to concrete in order to repair bond degradation or to provide anchorage for fresh concrete.

Cost Comparison of Refitting Against New Construction

The price of upgrading a historic building depends on a variety of criteria. Information gathering, specialized technical techniques, and unorthodox building materials are needed. The retrofit design may focus on one of four performance levels (prevention of collapse, safety of lives, immediate occupancy, and functionality), depending on the project's goals.

However, the actual results of the retrofitting may fall short of higher performance goals. Retrofitting costs can match or even exceed new construction premiums. Economic considerations are not the only ones taken into account when deciding whether to execute retrofits or Involved are sociopolitical, legal, and reconstruction factors. Architects and engineers' main contribution to the decision-making process is the provision of economic and technical data, although the final choice heavily depends on rules, politics, and historical values.

Seismic retrofitting is an important process that can help to keep buildings and other structures safe during an earthquake. If you’re looking to retrofit your building or structure, contact us for your seismic retrofitting plans www.jpcdesignconsortium.com/contact-us.